Collagenase treatment decreases muscle stiffness in cerebral palsy: A preclinical ex vivo biomechanical analysis of hip adductor muscle fiber bundles

AIM

To determine the dose-response relationship of collagenase Clostridium histolyticum (CCH) on collagen content and the change in muscle fiber bundle stiffness after ex vivo treatment of adductor longus biopsies with CCH in children with cerebral palsy (CP).

METHOD

Biopsy samples of adductor longus from children with CP (classified in Gross Motor Function Classification System levels IV and V) were treated with 0 U/mL, 200 U/mL, 350 U/mL, or 500 U/mL CCH; percentage collagen reduction was measured to determine the dose-response. Peak and steady-state stresses were determined at 1%, 2.5%, 5%, and 7.5% strain increments; Young's modulus was calculated.

RESULTS

Eleven patients were enrolled (nine males, two females, mean age at surgery 6 years 5 months; range: 2-16 years). A linear CCH dose-response relationship was determined. Peak and steady-state stress generation increased linearly at 5.9/2.3mN/mm2 , 12.4/5.3mN/mm2 , 22.2/9.7mN/mm2 , and 33.3/15.5mN/mm2 at each percentage strain increment respectively. After CCH treatment, peak and steady-state stress generation decreased to 3.2/1.2mN/mm2 , 6.5/2.9mN/mm2 , 12.2/5.7mN/mm2 , and 15.4/7.7mN/mm2 respectively (p < 0.004). Young's modulus decreased from 205 kPa to 100 kPa after CCH (p = 0.003).

INTERPRETATION

This preclinical ex vivo study provides proof of concept for the use of collagenase to decrease muscle stiffness in individuals with CP.

DNA Methylation Analysis Reveals Distinct Patterns in Satellite Cell-Derived Myogenic Progenitor Cells of Subjects with Spastic Cerebral Palsy

Spastic type cerebral palsy (CP) is a complex neuromuscular disorder that involves altered skeletal muscle microanatomy and growth, but little is known about the mechanisms contributing to muscle pathophysiology and dysfunction. Traditional genomic approaches have provided limited insight regarding disease onset and severity, but recent epigenomic studies indicate that DNA methylation patterns can be altered in CP. Here, we examined whether a diagnosis of spastic CP is associated with intrinsic DNA methylation differences in myoblasts and myotubes derived from muscle resident stem cell populations (satellite cells; SCs). Twelve subjects were enrolled (6 CP; 6 control) with informed consent/assent. Skeletal muscle biopsies were obtained during orthopedic surgeries, and SCs were isolated and cultured to establish patient-specific myoblast cell lines capable of proliferation and differentiation in culture. DNA methylation analyses indicated significant differences at 525 individual CpG sites in proliferating SC-derived myoblasts (MB) and 1774 CpG sites in differentiating SC-derived myotubes (MT). Of these, 79 CpG sites were common in both culture types. The distribution of differentially methylated 1 Mbp chromosomal segments indicated distinct regional hypo- and hyper-methylation patterns, and significant enrichment of differentially methylated sites on chromosomes 12, 13, 14, 15, 18, and 20. Average methylation load across 2000 bp regions flanking transcriptional start sites was significantly different in 3 genes in MBs, and 10 genes in MTs. SC derived MBs isolated from study participants with spastic CP exhibited fundamental differences in DNA methylation compared to controls at multiple levels of organization that may reveal new targets for studies of mechanisms contributing to muscle dysregulation in spastic CP.

Transcriptional analysis of muscle tissue and isolated satellite cells in spastic cerebral palsy

AIM

To analyze transcriptomes from muscle tissue and cells to improve our understanding of differences in gene expression and molecular function in cerebral palsy (CP) muscle.

METHOD

In this case-control study, eight participants with CP (five males, three females; mean [SD] age 14y 2mo [1y 8mo]) and 11 comparison individuals (eight males, three females; mean [SD] age 14y 0mo [2y 6mo]) were enrolled after informed consent/assent and skeletal muscle was obtained during surgery. RNA was extracted from tissue and from primary satellite cells grown to form myotubes in vitro. RNA sequencing data were analyzed using validated informatics pipelines.

RESULTS

Analysis identified expression of 6308 genes in the tissue samples and 7459 in the cultured cells. Significant differential expression between CP and control was identified in 87 genes in the tissue and 90 genes in isolated satellite cell-derived myotube cultures.

INTERPRETATION

Both tissue and cell analyses identified differential expression of genes associated with muscle development and multiple pathways of interest. What this paper adds Expression differences were found in muscle tissue and in isolated muscle cells. There was low variability in expression among cells isolated from different muscles. Expression differences suggest complex functional alterations in spastic cerebral palsy.

Human Adventitial Fibroblast Phenotype Depends on the Progression of Changes in Substrate Stiffness

Adventitial fibroblasts (AFs) are major contributors to vascular remodeling and maladaptive cascades associated with arterial disease, where AFs both contribute to and respond to alterations in their surrounding matrix. The relationships between matrix modulus and human aortic AF (AoAF) function are investigated using poly(ethylene glycol)-based hydrogels designed with matrix metalloproteinase (MMP)-sensitive and integrin-binding peptides. Initial equilibrium shear storage moduli for the substrates examined are 0.33, 1.42, and 2.90 kPa; after 42 days of culture, all hydrogels exhibit similar storage moduli (0.3-0.7 kPa) regardless of initial modulus, with encapsulated AoAFs spreading and proliferating. In 10 and 7.5 wt% hydrogels, modulus decreases monotonically throughout culture; however, in 5 wt% hydrogels, modulus increases after an initial 7 days of culture, accompanied by an increase in myofibroblast transdifferentiation and expression of collagen I and III through day 28. Thereafter, significant reductions in both collagens occur, with increased MMP-9 and decreased tissue inhibitor of metalloproteinase-1/-2 production. Releasing cytoskeletal tension or inhibiting cellular protein secretion in 5 wt% hydrogels block the stiffening of the polymer matrix. Results indicate that encapsulated AoAFs initiate cell-mediated matrix remodeling and demonstrate the utility of dynamic 3D systems to elucidate the complex interactions between cell behavior and substrate properties.

Epigenetic machine learning: utilizing DNA methylation patterns to predict spastic cerebral palsy

BACKGROUND

Spastic cerebral palsy (CP) is a leading cause of physical disability. Most people with spastic CP are born with it, but early diagnosis is challenging, and no current biomarker platform readily identifies affected individuals. The aim of this study was to evaluate epigenetic profiles as biomarkers for spastic CP. A novel analysis pipeline was employed to assess DNA methylation patterns between peripheral blood cells of adolescent subjects (14.9 ± 0.3 years old) with spastic CP and controls at single CpG site resolution.

RESULTS

Significantly hypo- and hyper-methylated CpG sites associated with spastic CP were identified. Nonmetric multidimensional scaling fully discriminated the CP group from the controls. Machine learning based classification modeling indicated a high potential for a diagnostic model, and 252 sets of 40 or fewer CpG sites achieved near-perfect accuracy within our adolescent cohorts. A pilot test on significantly younger subjects (4.0 ± 1.5 years old) identified subjects with 73% accuracy.

CONCLUSIONS

Adolescent patients with spastic CP can be distinguished from a non-CP cohort based on DNA methylation patterns in peripheral blood cells. A clinical diagnostic test utilizing a panel of CpG sites may be possible using a simulated classification model. A pilot validation test on patients that were more than 10 years younger than the main adolescent cohorts indicated that distinguishing methylation patterns are present earlier in life. This study is the first to report an epigenetic assay capable of distinguishing a CP cohort.

Reduced arterial elasticity due to surgical skeletonization is ameliorated by abluminal PEG hydrogel

Arteries for bypass grafting are harvested either with neighboring tissue attached or as skeletonized vessels that are free of surrounding tissue. There are significant benefits to skeletonization, but reports suggest that skeletonized vessels may develop structural defects and are at risk for atherosclerosis. We investigated the specific short‐term effects of skeletonization on carotid artery biomechanics and microanatomy in a rabbit model. Six carotid arteries were surgically skeletonized. To support healing, three of these received polyethylene glycol hydrogel injected along their exterior surfaces. M‐mode ultrasonography was used to track circumferential cyclic strain in the skeletonized, hydrogel‐treated, and contralateral vessels. On day 21, the arteries were harvested, and vessel structure was assessed by histology, immunofluorescence microscopy, two‐photon elastin autofluorescence, and second harmonic generation (SHG) microscopy. Intimal‐medial thickness appeared unaffected by skeletonization, but the SHG signals indicated significant changes in collagen turnover in the adventitia. Skeletonized arteries also exhibited significantly decreased radial compliance (circumferential cyclic strain dropped ∼30%) and decreased numbers of elastic laminae (9.1 ± 2.0 to 2.3 ± 1.4). Hydrogel treatment protected against these effects with treated vessels maintaining normal mechanical properties. These results indicate that arterial skeletonization triggers immediate effects on vessel remodeling and reduced vessel compliance resulting in specific tissue alterations within 21 days, but that these effects can be attenuated by the placement of hydrogel on the exterior surface of the skeletonized vessel.

Decreasing matrix modulus of PEG hydrogels induces a vascular phenotype in human cord blood stem cells

Adult and congenital cardiovascular diseases are significant health problems that are often managed using surgery. Bypass grafting is a principal therapy, but grafts fail at high rates due to hyperplasia, fibrosis, and atherosclerosis. Biocompatible, cellularized materials that attenuate these complications and encourage healthy microvascularization could reduce graft failure, but an improved understanding of biomaterial effects on human stem cells is needed to reach clinical utility. Our group investigates stem-cell-loaded biomaterials for placement along the adventitia of at-risk vessels and grafts. Here, the effects of substrate modulus on human CD34+ stem cells from umbilical cord blood were evaluated. Cells were isolated by immunomagnetic separation and encapsulated in 3, 4, and 6 weight% PEG hydrogels containing 0.032% gelatin and 0.0044% fibronectin. Gels reached moduli of 0.34, 4.5, and 9.1 kPa. Cell viability approached 100%. Cell morphologies appeared similar across gels, but proliferation was significantly lower in 6 wt% gels. Expression profiling using stem cell signaling arrays indicated enhanced self-renewal and differentiation into vascular endothelium among cells in the lower weight percent gels. Thus, modulus was associated with cell proliferation and function. Gels with moduli in the low kilopascal range may be useful in stimulating cell engraftment and microvascularization of graft adventitia.

Disruption of basal lamina components in neuromotor synapses of children with spastic quadriplegic cerebral palsy

Cerebral palsy (CP) is a static encephalopathy occurring when a lesion to the developing brain results in disordered movement and posture. Patients present with sometimes overlapping spastic, athetoid/dyskinetic, and ataxic symptoms. Spastic CP, which is characterized by stiff muscles, weakness, and poor motor control, accounts for ∼80% of cases. The detailed mechanisms leading to disordered movement in spastic CP are not completely understood, but clinical experience and recent studies suggest involvement of peripheral motor synapses. For example, it is recognized that CP patients have altered sensitivities to drugs that target neuromuscular junctions (NMJs), and protein localization studies suggest that NMJ microanatomy is disrupted in CP. Since CP originates during maturation, we hypothesized that NMJ disruption in spastic CP is associated with retention of an immature neuromotor phenotype later in life. Scoliosis patients with spastic CP or idiopathic disease were enrolled in a prospective, partially-blinded study to evaluate NMJ organization and neuromotor maturation. The localization of synaptic acetylcholine esterase (AChE) relative to postsynaptic acetylcholine receptor (AChR), synaptic laminin β2, and presynaptic vesicle protein 2 (SV2) appeared mismatched in the CP samples; whereas, no significant disruption was found between AChR and SV2. These data suggest that pre- and postsynaptic NMJ components in CP children were appropriately distributed even though AChE and laminin β2 within the synaptic basal lamina appeared disrupted. Follow up electron microscopy indicated that NMJs from CP patients appeared generally mature and similar to controls with some differences present, including deeper postsynaptic folds and reduced presynaptic mitochondria. Analysis of maturational markers, including myosin, syntrophin, myogenin, and AChR subunit expression, and telomere lengths, all indicated similar levels of motor maturation in the two groups. Thus, NMJ disruption in CP was found to principally involve components of the synaptic basal lamina and subtle ultra-structural modifications but appeared unrelated to neuromotor maturational status.

Neuromotor synapses in Escobar syndrome

The Escobar variant of multiple pterygium syndrome (OMIM #265000) is a rare, autosomal recessive disorder associated with mutations in the γ-subunit of the nicotinic acetylcholine receptor (CHRNG). CHRNG is expressed in fetal muscle during motor development and contributes to the formation of neuromuscular junctions (NMJs). Anomalies in NMJ structure and function have not been investigated in patients with Escobar syndrome. We report five patients identified as having Escobar syndrome, from four families. In three families, the same mutation (c.459dupA) was identified in CHRNG. A biopsy from brachioradialis muscle was collected from a patient from one of these families and analyzed for NMJ organization using fluorescence microscopy. Compared to spinalis muscle from control patients with idiopathic scoliosis or cerebral palsy (CP), the patient with Escobar syndrome had a significantly higher degree of acetylcholine receptor present outside acetylcholinesterase and significantly less acetylcholinesterase outside acetylcholine receptors. Given the role of the acetylcholine receptor γ-subunit in fetal neuromuscular signal transduction and in establishing the primary encounter of muscle and motor nerve terminal, the CHRNG mutations described in Escobar syndrome may cause a broader disruption of postsynaptic proteins and result in aberrant development of the NMJ due to impaired prenatal neuromuscular transmission and/or abnormal neuromuscular synaptogenesis.

In situ crosslinkable heparin-containing poly(ethylene glycol) hydrogels for sustained anticoagulant release

Low-molecular weight heparin (LMWH) is widely used in anticoagulation therapies and for the prevention of thrombosis. LMWH is administered by subcutaneous injection usually once or twice per day. This frequent and invasive delivery modality leads to compliance issues for individuals on prolonged therapeutic courses, particularly pediatric patients. Here, we report a long-term delivery method for LMWH via subcutaneous injection of long-lasting hydrogels. LMWH is modified with reactive maleimide groups so that it can be crosslinked into continuous networks with four-arm thiolated poly(ethylene glycol) (PEG-SH). Maleimide-modified LMWH (Mal-LMWH) retains bioactivity as indicated by prolonged coagulation time. Hydrogels comprising PEG-SH and Mal-LMWH degrade via hydrolysis, releasing bioactive LMWH by first-order kinetics with little initial burst release. Separately dissolved Mal-LMWH and PEG-SH solutions were co-injected subcutaneously in New Zealand White rabbits. The injected solutions successfully formed hydrogels in situ and released LMWH as measured via chromogenic assays on plasma samples, with accumulation of LMWH occurring at day 2 and rising to near-therapeutic dose equivalency by day 5. These results demonstrate the feasibility of using LMWH-containing, crosslinked hydrogels for sustained and controlled release of anticoagulants.

Differential effects of substrate modulus on human vascular endothelial, smooth muscle, and fibroblastic cells

Regenerative medicine approaches offer attractive alternatives to standard vascular reconstruction; however, the biomaterials to be used must have optimal biochemical and mechanical properties. To evaluate the effects of biomaterial properties on vascular cells, heparinized poly(ethylene glycol) (PEG)-based hydrogels of three different moduli, 13.7, 5.2, and 0.3 kPa, containing fibronectin and growth factor were utilized to support the growth of three human vascular cell types. The cell types exhibited differences in attachment, proliferation, and gene expression profiles associated with the hydrogel modulus. Human vascular smooth muscle cells demonstrated preferential attachment on the highest-modulus hydrogel, adventitial fibroblasts demonstrated preferential growth on the highest-modulus hydrogel, and human umbilical vein endothelial cells demonstrated preferential growth on the lowest-modulus hydrogel investigated. Our studies suggest that the growth of multiple vascular cell types can be supported by PEG hydrogels and that different populations can be controlled by altering the mechanical properties of biomaterials.

Reduction of hexavalent uranium from organic complexes by sulfate- and iron-reducing bacteria

The influence of organic-hexavalent-uranium [U(VI)] complexation on U(VI) reduction by a sulfate-reducing bacterium (Desulfovibrio desulfuricans) and an iron-reducing bacterium (Shewanella alga) was evaluated. Four aliphatic ligands (acetate, malonate, oxalate, and citrate) and an aromatic ligand (tiron [4,5-dihydroxy-1,3-benzene disulfonic acid]) were used to study complexed-uranium bioavailability. The trends in uranium reduction varied with the nature and the amount of U(VI)-organic complex formed and the type of bacteria present. D. desulfuricans rapidly reduced uranium from a monodentate aliphatic (acetate) complex. However, reduction from multidentate aliphatic complexes (malonate, oxalate, and citrate) was slower. A decrease in the amount of organic-U(VI) complex in solution significantly increased the rate of reduction. S. alga reduced uranium more rapidly from multidentate aliphatic complexes than from monodentate aliphatic complexes. The rate of reduction decreased with a decrease in the amount of multidentate complexes present. Uranium from an aromatic (tiron) complex was readily available for reduction by D. desulfuricans, while an insignificant level of U(VI) from the tiron complex was reduced by S. alga. These results indicate that selection of bacteria for rapid uranium reduction will depend on the organic composition of waste streams.

Three-dimensional culture alters primary cardiac cell phenotype

The directed formation of complex three-dimensional (3D) tissue architecture is a fundamental goal in tissue engineering and regenerative medicine. The growth of cells in 3D structures is expected to influence cellular phenotype and function, especially relative cell distribution, expression profiles, and responsiveness to exogenous signals; however, relatively few studies have been carried out to examine the effects of 3D reaggregation on cells from critical target organs, like the heart. Accordingly, we cultured primary cardiac ventricular cells in a 3D model system using a serum-free medium to test the hypothesis that expression profiles, multicellular organizational pathways, tissue maturation markers, and responsiveness to hormone stimulation were significantly altered in stable cell populations grown in 3D versus 2D culture. We found that distinct multi-cellular structures formed in 3D in conjunction with changes in mRNA expression profile, up-regulation of endothelial cell migratory pathways, decreases in the expression of fetal genes (Nppa and Ankrd1), and increased sensitivity to tri-iodothyronine stimulation when compared to parallel 2D cultures comprising the same cell populations. These results indicate that the culture of primary cardiac cells in 3D aggregates leads to physiologically relevant alterations in component cell phenotype consistent with cardiac ventricular tissue formation and maturation.

Robust quantification of the SMN gene copy number by real-time TaqMan PCR

Spinal muscular atrophy (SMA) is an autosomal recessive disease caused by mutation or deletion of the survival motor neuron gene 1 (SMN1). The highly homologous gene, SMN2, is present in all patients, but it cannot compensate for loss of SMN1. SMN2 differs from SMN1 by a few nucleotide changes, but a C --> T transition in exon 7 leads to exon skipping. As a result, most transcripts from the SMN2 gene lack exon 7. Although SMN1 is the disease-determining gene, the number of SMN2 copies appears to modulate SMA clinical phenotypes. Thus, determining the SMN copy number is important for clinical diagnosis and prognosis. We have developed a quantitative real-time TaqMan polymerase chain reaction assay for both the SMN1 and SMN2 genes, in which reliable copy number determination was possible on deoxyribonucleic acid samples obtained by two different isolation methods and from two different sources (human blood and skin fibroblasts). For SMN1, allele specificity was attained solely by addition of an allele-specific forward primer and, for SMN2, by addition of a specific forward primer and a nonextending oligonucleotide (SMN1 blocker) that reduced nonspecific amplification from SMN1 to a negligible level. We validated the reliability of this real-time polymerase chain reaction approach and found that the coefficient of variation for all the gene copy number measurements was below 10%. Quantitative analysis of the SMN copy number in SMA fibroblasts by this approach showed deletion of SMN1 and an inverse correlation between the SMN2 copy number and severity of the disease.

Molecular assessment of ammonia- and nitrite-oxidizing bacteria in full-scale activated sludge wastewater treatment plants

Nitrification was assessed in two full-scale wastewater treatment plants (WWTPs) over time using molecular methods. Both WWTPs employed a complete-mix suspended growth, aerobic activated sludge process (with biomass recycle) for combined carbon and nitrogen treatment. However, one facility treated primarily municipal wastewater while the other only industrial wastewater. Real time PCR assays were developed to determine copy numbers for total 16S rDNA (a measure of biomass content), the amoA gene (a measure of ammonia-oxidizers), and the Nitrospira 16S rDNA gene (a measure of nitrite-oxidizers) in mixed liquor samples. In both the municipal and industrial WWTP samples, total 16S rDNA values were approximately 2-9 x 10(13) copies/L and Nitrospira 16S rDNA values were 2-4 x 10(10) copies/L. amoA gene concentrations averaged 1.73 x 10(9) copies/L (municipal) and 1.06 x 10(10) copies/L (industrial), however, assays for two distinct ammonia oxidizing bacteria were required.

Quantification of Nitrosomonas oligotropha and Nitrospira spp. using competitive polymerase chain reaction in bench-scale wastewater treatment reactors operating at different solids retention times

The effect of solids retention time (SRT) on ammonia-and nitrite-oxidizing bacteria was measured by Nitrosomonas oligotropha-like ammonia monooxygenase A and Nitrospira 16S rDNA competitive polymerase chain reaction assays in a complete-mix, bench-scale, activated-sludge system. During steady-state operation, nitrification was complete in the 20- and 10-day SRT reactors, nearly complete in the 5-day SRT reactor, and incomplete in the 2-day SRT reactor (76% ammonia oxidation and 85% nitrite oxidation). Total microbes, measured by dot-blot hybridizations, ranged from 3 x 10(11) to 3 x 10(12) cells/L, and increased with increasing SRTs. The concentration of the ammonia-oxidizer N. oligotropha dropped 100-fold from the 20-day SRT (5 x 10(9) cells/L) to the 2-day SRT (< or = 4 x 10(7) cells/L). Thus, N. oligotropha became a much smaller fraction of the total biomass in the poorly performing 2-day SRT reactor. The concentration of Nitrospira cells also decreased (10-fold) as the SRT was reduced from 20 days to 2 days. However, the number of Nitrospira cells was always greater than the number of N. oligotropha cells measured in each reactor (10- to 60-fold). While Nitrospira comprised 1 to 2% of the biomass, N. oligotropha represented only 0.04 to 0.27% of the total population. This low percentage suggests that N. oligotropha was not a dominant ammonia oxidizer in the bench-scale systems.

The measurement of toluene dioxygenase activity in biofilm culture of Pseudomonas putida F1

Toluene dioxygenase (Tod) enzyme activity can be measured by the conversion of indole to indigo. Indigo is measured spectrophotometrically at 600 nm. However, this method is inadequate to measure the whole-cell enzyme activity when interference by suspended biomass is present. Indoxyl is a highly fluorescent intermediate in the conversion of indole to indigo by Tod. A fluorescence-based assay was developed and applied to monitor Tod activity in whole cells of Pseudomonas putida F1 biofilm from a continuously operated biofilter. Suspended growth studies with pure cultures indicated that indoxyl, as measured by fluorescence, correlated with indigo production (r(2)=0.89) as measured by spectrophotometry. Whole-cell enzyme activity was followed during growth on a minimal medium containing toluene. The maximum normalized whole cell enzyme activity of 19+/-1.5x10(-4) mg indigo (mg protein)(-1) min(-1) was reached during early stationary phase. P. putida F1 cells from a biofilm grown on vapor phase toluene had a normalized whole-cell enzyme activity of 5.0+/-0.2x10(-4) mg indigo (mg protein)(-1) min(-1). The half-life of whole-cell enzyme activity was estimated to be between 5.5 and 8 h in both suspended and biofilm growth conditions.

Myocardial osteopontin expression coincides with the development of heart failure

To identify genes that are differentially expressed during the transition from compensated hypertrophy to failure, myocardial mRNA from spontaneously hypertensive rats (SHR) with heart failure (SHR-F) was compared with that from age-matched SHR with compensated hypertrophy (SHR-NF) and normotensive Wistar-Kyoto rats (WKY) by differential display reverse transcriptase-polymerase chain reaction. Characterization of a transcript differentially expressed in SHR-F yielded a cDNA with homology to the extracellular matrix protein osteopontin. Northern analysis showed low levels of osteopontin mRNA in left ventricular myocardium from WKY and SHR-NF but a markedly increased (approximately 10-fold) level in SHR-F. In myocardium from WKY and SHR-NF, in situ hybridization showed only scant osteopontin mRNA, primarily in arteriolar cells. In SHR-F, in situ hybridization revealed abundant expression of osteopontin mRNA, primarily in nonmyocytes in the interstitial and perivascular space. Similar findings for osteopontin protein were observed in the midwall region of myocardium from the SHR-F group. Consistent with the findings in SHR, osteopontin mRNA was minimally increased (approximately 1.9-fold) in left ventricular myocardium from nonfailing aortic-banded rats with pressure-overload hypertrophy but was markedly increased (approximately 8-fold) in banded rats with failure. Treatment with captopril starting before or after the onset of failure in the SHR reduced the increase in left ventricular osteopontin mRNA levels. Thus, osteopontin expression is markedly increased in the heart coincident with the development of heart failure. The source of osteopontin in SHR-F is primarily nonmyocytes, and its induction is inhibited by an angiotensin-converting enzyme inhibitor, suggesting a role for angiotensin II. Given the known biological activities of osteopontin, including cell adhesion and regulation of inducible nitric oxide synthase gene expression, these data suggest that it could play a role in the pathophysiology of heart failure.

Direct effects of colchicine on myocardial function: studies in hypertrophied and failing spontaneously hypertensive rats

-The aging spontaneously hypertensive rat (SHR) is a model in which the transition from chronic stable left ventricular hypertrophy to overt heart failure can be observed. Although the mechanisms for impaired function in hypertrophied and failing cardiac muscle from the SHR have been studied, none accounts fully for the myocardial contractile abnormalities. The cardiac cytoskeleton has been implicated as a possible cause for myocardial dysfunction. If an increase in microtubules contributes to dysfunction, then myocardial microtubule disruption by colchicine should promote an improvement in cardiac performance. We studied the active and passive properties of isolated left ventricular papillary muscles from 18- to 24-month-old SHR with evidence of heart failure (SHR-F, n=6), age-matched SHR without heart failure (SHR-NF, n=6), and age-matched normotensive Wistar-Kyoto rats (WKY, n=5). Mechanical parameters were analyzed before and up to 90 minutes after the addition of colchicine (10(-5), 10(-4), and 10(-3) mol/L). In the baseline state, active tension (AT) developed by papillary muscles from the WKY group was greater than for SHR-NF and SHR-F groups (WKY 5.69+/-1.47 g/mm2 [mean+/-SD], SHR-NF 3.41+/-1.05, SHR-F 2.87+/-0.26; SHR-NF and SHR-F P<0.05 versus WKY rats). The passive stiffness was greater in SHR-F than in the WKY and SHR-NF groups (central segment exponential stiffness constant, Kcs: SHR-F 70+/-25, SHR-NF 44+/-17, WKY 41+/-13 [mean+/-SD]; SHR-F P<0.05 versus SHR-NF and WKY rats). AT did not improve after 10, 20, and 30 minutes of exposure to colchicine (10(-5), 10(-4), and 10(-3) mol/L) in any group. In the SHR-F group, AT and passive stiffness did not change after 30 to 90 minutes of colchicine exposure (10(-4) mol/L). In summary, the data in this study fail to demonstrate improvement of intrinsic muscle function in SHR with heart failure after colchicine. Thus, in the SHR there is no evidence that colchicine-induced cardiac microtubular depolymerization affects the active or passive properties of hypertrophied or failing left ventricular myocardium.

Effect of angiotensin-converting enzyme inhibition on myocardial fibrosis and function in hypertrophied and failing myocardium from the spontaneously hypertensive rat

BACKGROUND

After a period of stable hypertrophy, male spontaneously hypertensive rats (SHR) develop heart failure between 18 to 24 months of age, with depression of active myocardial function and increased passive stiffness. We tested the hypothesis that chronic ACE inhibition by captopril would prevent and possibly reverse impairment of myocardial function.

METHODS AND RESULTS

Male SHR and normotensive Wistar-Kyoto rats (WKY) were assigned to no treatment or captopril treatment (2 g/L in drinking water) begun at ages 12, 18, and 21 months; animals were studied at 24 months of age, or earlier when evidence of heart failure was found in SHR (mean age, 19+/-2 months). In an additional group, captopril treatment was begun when SHR developed heart failure; surviving animals were studied at 24 months of age. In untreated SHR, relative to WKY, isometric stress development at Lmax, maximum rate of stress development, and shortening velocity were depressed, whereas passive stiffness was increased, in association with the development of myocardial fibrosis. In the SHR treated before cardiac dysfunction, captopril administration attenuated hypertrophy and prevented contractile dysfunction, fibrosis, and increased passive stiffness. Captopril treatment begun after cardiac function was impaired reduced left ventricular hypertrophy but did not restore intrinsic contractile function or reduce fibrosis or passive stiffness.

CONCLUSIONS

In the male SHR, early treatment with captopril was associated with the most marked attenuation of dysfunction relative to the untreated SHR. Treatment initiated after the onset of heart failure improved clinical signs of heart failure and decreased left ventricular hypertrophy in surviving animals but did not reverse the fibrosis and contractile dysfunction associated with heart failure.

[Role of myocardial contractile status and relaxation in ventricular dysfunction during the transition of heart hypertrophy to failure]

PURPOSE

To investigate the participation of contractile state and relaxation in cardiac muscle dysfunction during the transition from stable hypertrophy to cardiac decompensation in aging spontaneously hypertensive rats (SHR).

METHODS

Isolated left ventricular papillary muscle function was studied in SHR with heart failure (SHR-F), in age-matched SHR without evidence of heart failure (SHR-NF), and in nonhypertensive controls Wistar-Kyoto rats (WKY). Muscles were analysed in isometric and isotonic contractions in Krebs-Henseleit solution with calcium concentration of 1.25 mM at 28 degrees C.

RESULTS

Papillary muscles from SHR-F and SHR-NF demonstrated decreased active tension development and shortening velocity relative to normotensive WKY (p < 0.05). SHR-F and SHR-NF did not differ. Compared with SHR-NF and WKY, muscle passive stiffness was increased in the failing SHR (p < 0.05 versus WKY and SHR-NF). This parameter did not differ between SHR-NF and WKY (p > 0.05).

CONCLUSION

These data suggest that the progression from stable hypertrophy to heart failure is associated with changes in the passive stiffness and is not related to depression of myocardial contractile function.

Localization of alpha1(I) collagen mRNA in myocardium from the spontaneously hypertensive rat during the transition from compensated hypertrophy to failure

Spontaneously hypertensive rats (SHR) commonly develop impairment of myocardial function between ages 18-24 months. Isolated muscle studies demonstrate depressed myocardial contractility and increased passive stiffness. Studies of the extracellular matrix in SHR with failure (SHR-F) demonstrate an increased expression of genes encoding extracellular matrix components (ECM), hydroxyproline concentration and fibrosis relative to age-matched non-failing animals. In the present study, tissue sections of hearts from SHR-F, non-failing SHR (SHR-NF) and non-hypertensive Wistar Kyoto rats (WKY) were hybridized with a cDNA probe for alpha1(I) collagen mRNA, which was found by Northern blot analysis to be elevated in SHR-F relative to hearts from control animals. In situ hybridization studies demonstrate increased perivascular and interstitial collagen alpha1(I) gene expression in myocardium from the SHR relative to WKY. In addition, failing hearts from the SHR demonstrate focal alpha1(I) collagen mRNA accumulation in the endocardium and at sites of degenerating single myocardial cells.

Increased cardiomyocyte apoptosis during the transition to heart failure in the spontaneously hypertensive rat

The transition from compensated hypertrophy to failure in spontaneously hypertensive rats (SHR) of advanced age is associated with a marked increase in collagen, a reduction in myocyte mass, and a reduction in maximum Ca(2+)-activated myofibrillar force. We hypothesized that the reduction in myocyte mass and associated functional loss may be due to increased cell death by apoptosis. To test this hypothesis, we studied hearts from failing (SHR-F) and nonfailing SHR (SHR-NF) and age-matched Wistar-Kyoto rats (WKY). In addition, hearts from SHR-F that had been treated with an angiotensin-converting enzyme inhibitor (captopril) for an average of 27 days were also studied. Apoptotic cells were quantified in cross sections of myocardium by the terminal deoxynucleotidyltransferase- mediated 2'-deoxyuridine 5'-triphosphate nick end labeling technique. To identify the type of the cells undergoing apoptosis, sections were also stained for alpha-sarcomeric actin. Apoptotic cells were significantly increased in the SHR-F (38.92 +/- 12.79 vs. 8.05 +/- 3.98 cells/100,000 nuclei in SHR-NF; P < 0.05 and vs. 2.21 +/- 1.4 cells/100,000 nuclei in WKY; P < 0.01). Captopril treatment of SHR-F reduced the number of apoptotic cells to the level in SHR-NF (9.17 +/- 1.53 cells/100,000 nuclei; P < 0.01 vs. SHR-F). Most apoptotic cells were of cardiac myocyte origin. There was no significant difference in Bcl-2 protein expressed by hearts among the three groups. WAF-1 mRNA levels were increased in both SHR groups vs. WKY; in SHR-F, the density of WAF-1 mRNA was higher than in SHR-NF. Thus increased numbers of apoptotic cells are present in failing SHR hearts, suggesting that apoptosis might be a mechanism involved in the reduction of myocyte mass that accompanies the transition from stable compensation to heart failure in this model. Administration of the angiotensin-converting enzyme inhibitor captopril, which ameliorates heart failure in this model, is associated with a reduction in the exaggerated apoptosis that accompanies heart failure.

Effect of chronic colchicine administration on the myocardium of the aging spontaneously hypertensive rat

Colchicine has been demonstrated to suppress the release of fibroblast growth factors, retard collagen formation and augment collagenase activity. Trials with colchicine in patients with hepatic fibrosis have suggested clinical benefit. The development of impaired myocardial function in the spontaneously hypertensive rat (SHR) is associated with a marked increase in myocardial fibrosis. The present study was carried out to test the hypothesis that chronic colchicine administration to the SHR would prevent the development of fibrosis and impaired myocardial performance. Colchicine (1 mg/l drinking water) was administered to male SHR and WKY rats from at age 13 months until 24 months or until evidence of heart failure was observed. Age-matched untreated SHR and colchicine treated and untreated WKY served as controls. At study, active and passive properties of isolated left ventricular muscle preparations were determined. Myocardial fibrosis was assessed by measuring hydroxyproline and histologic determination of interstitial cross-sectional area. Increases in LV hydroxyproline and interstitial area were found in untreated SHR relative to WKY; passive myocardial stiffness was increased and active muscle properties were depressed. In comparing colchicine treated vs untreated SHR, no differences in hydroxyproline, interstitial area or intrinsic myocardial function were found. In the WKY, colchicine increased myocardial interstitium and passive stiffness without changing hydroxyproline. Active myocardial function was not depressed. Thus, chronic colchicine administration neither attenuated the development of interstitial fibrosis nor prevented impaired myocardial function in the SHR. Colchicine treatment was associated with increased interstitium in WKY with increased passive myocardial stiffness.

Modulation of left and right ventricular beta-adrenergic receptors from spontaneously hypertensive rats with left ventricular hypertrophy and failure

Inotropic responsiveness to beta-adrenergic stimulation is generally found to be depressed in cardiac hypertrophy and failure. To investigate whether inotropic responsiveness is associated with alterations in beta-adrenergic receptors in spontaneously hypertensive rats (SHR), we studied left ventricular myocardial contractile responses to isoproterenol and beta-adrenergic receptor density and affinity in age-matched rats (18 to 24 months), including SHR without heart failure, SHR with evidence of heart failure, and normotensive control Wistar-Kyoto rats (WKY). In the baseline state, papillary muscles from failing SHR demonstrated decreased isometric tension development and a reduction in maximal rate of tension development relative to normotensive WKY and compensated SHR. Compared with WKY, beta-adrenergic receptor density of the left ventricle was unchanged in nonfailing SHR and increased in failing SHR (P < .05 versus WKY and nonfailing SHR), and beta-adrenergic receptor affinity did not differ among groups. In the right ventricle, beta-adrenergic receptor density was decreased in failing SHR relative to WKY and nonfailing SHR, and beta-adrenergic receptor affinity was not different among groups. Muscle preparations did not exhibit a positive inotropic response to 10(-8) to 10(-5) mol/L isoproterenol or 6.3 mumol/L forskolin in either failing or nonfailing SHR, whereas a positive inotropic response to both drugs was observed in the normotensive WKY. The lusitropic response to isoproterenol and forskolin was intact and similar in both SHR groups and WKY. The findings suggest that in the SHR model of heart failure, impaired intrinsic left ventricular myocardial function and depressed inotropic responsiveness to beta-adrenergic stimulation are not associated with downregulation of the beta-adrenergic receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

The spontaneously hypertensive rat as a model of the transition from compensated left ventricular hypertrophy to failure

Studies of hemodynamics and intrinsic left ventricular myocardial function are carried out to investigate the transition from stable hypertrophy to cardiac decompensation in the aging (18-24 months) spontaneously hypertensive rat (SHR). Echocardiographic data in awake animals demonstrate increased end-diastolic and end-systolic volumes and depressed ejection fractions in left ventricles from SHR with failure (SHR-F) as compared to age matched hypertensive (SHR-NF) and non-hypertensive control animals (WKY). Cardiac catheterization data in anesthetized animals demonstrate depression of both systolic pressure and +dP/dt, and elevated end-diastolic pressure in the SHR-F relative to the two control groups. Since loading conditions and altered demand states may contribute to altered ventricular function, studies of isolated perfused hearts were carried out which demonstrate impaired systolic stress development in the SHR-F group under conditions in which loading conditions are controlled; in addition, it is observed that increasing perfusion pressure by 30 mm Hg has little effect on function. Depression of systolic function and increases in passive stiffness of isolated muscle preparations from the SHR-F indicate impairment of systolic and diastolic function at the tissue level. While all of the preparations studied have potential shortcomings, an integration of findings from these complementary approaches supports the conclusion that heart failure develops in the aging SHR. Furthermore, these data suggest that impaired function is due to changes in the intrinsic properties of the myocardium and that the connective tissue response may play an important role. These studies, in conjunction with the findings of others who have studied the aging SHR, provide support for the use of the aging SHR as a model of the transition from compensated hypertrophy to failure.

Myocardial fibrosis and stiffness with hypertrophy and heart failure in the spontaneously hypertensive rat

BACKGROUND

Fibrosis is commonly found in association with cardiac hypertrophy and failure, but the relation of the connective tissue response to the development of impaired cardiac function remains unclear. We examined passive myocardial stiffness, active contractile function, and fibrosis in the spontaneously hypertensive rat (SHR), a model of chronic pressure overload in which impaired cardiac function follows a long period of stable hypertrophy.

METHODS AND RESULTS

We studied the passive and active mechanical properties of left ventricular (LV) papillary muscles isolated from normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) at the ages of 12 months and 20 to 23 months. Seven of 15 SHR between 20 and 23 months of age had findings consistent with heart failure (SHR-F). In comparison to preparations from WKY rats and nonfailing SHR (SHR-NF), papillary muscles from the SHR-F group demonstrated increased passive stiffness (central segment exponential stiffness constant, kcs: SHR-F 95.6 +/- 19.8, SHR-NF 42.1 +/- 9.7, WKY rats 39.5 +/- 9.5 (mean +/- SD); SHR-F P < .01 versus SHR-NF, WKY rats). The increase in stiffness was associated with an increase in LV collagen concentration (SHR-F 8.71 +/- 3.14, SHR-NF 5.83 +/- 1.20, WKY rats 4.78 +/- 0.70 mg hydroxyproline/g dry LV wt; SHR-F P < .01 versus SHR-NF, WKY rats); an increase in interstitial fibrosis, as determined histologically (SHR-F 13.5 +/- 8.0%, SHR-NF 4.9 +/- 2.1%, WKY rats 3.6 +/- 0.8%; SHR-F P < .01 versus SHR-NF, WKY rats); and impaired tension development (SHR-F 3.18 +/- 1.27, SHR-NF 4.41 +/- 1.04, WKY rats 4.64 +/- 0.85 kdyne/mm2; SHR-F P < .05 versus SHR-NF; P < .01 versus WKY rats).

CONCLUSIONS

The development of heart failure in the aging SHR is associated with marked myocardial fibrosis, increased passive stiffness, and impaired contractile function relative to age-matched nonfailing SHR and nonhypertensive control animals. These data suggest that fibrosis or events underlying the connective tissue response are important in the transition from compensated hypertrophy to failure in the SHR.

Protective effects of diltiazem on the mechanical performance of the hypoxic myocardium

1. To determine whether diltiazem protects the hypoxic myocardium by reducing contractile work, we have compared the effects of diltiazem and quiescence on left ventricular (LV) papillary muscle subjected to hypoxia. Papillary muscles were obtained from male Charles River CD rats weighing 150-250 g. 2. Four groups of muscles were studied: control (N = 6), non-stimulation (N = 10), diltiazem 10(-4) M (N = 6) and diltiazem 10(-4) M plus non-stimulation (N = 10). 3. Isolated rat LV papillary muscles were studied in Krebs-Henseleit solution with a calcium concentration of 2.52 mM at 28 degrees C while contracting isometrically at a stimulation rate of 0.2 Hz. Resting tension and active isometric tension were measured. 4. Both diltiazem and quiescence significantly attenuated contracture tension during hypoxia (0.91 +/- 0.10 vs 2.26 +/- 0.49 g/mm2 for diltiazem vs control, and 0.55 +/- 0.18 vs 2.26 +/- 0.49 g/mm2 for quiescence vs control). Recovery of active tension was improved in the diltiazem groups during reoxygenation (4.16 +/- 0.42 vs 3.75 +/- 0.51, 3.53 +/- 0.15 vs 2.90 +/- 0.13, 5.84 +/- 0.33 vs 6.48 +/- 0.29 and 5.98 +/- 0.90 vs 7.67 +/- 0.68 g/mm2 for diltiazem, diltiazem non-stimulation, non-stimulation and control groups). 5. The results suggest that the protective effect of diltiazem during hypoxia was due to the reduction in energy demand of the myocardium.

Impaired myocardial function in spontaneously hypertensive rats with heart failure

We have observed that many spontaneously hypertensive rats (SHR) between the ages of 18 and 24 mo develop findings suggestive of heart failure, including pleural and pericardial effusions, left atrial thrombi, and right ventricular hypertrophy. Isolated left ventricular papillary muscle function was studied in these animals (SHR-F), in age-matched SHRs without evidence of heart failure (SHR-NF), and in nonhypertensive controls (WKY). Preparations from SHR-F showed depression of active tension development (3.58 +/- 1.75 g/mm2, means +/- SD) compared with both SHR-NF (7.17 +/- 0.94) and WKY (6.17 +/- 1.00) (P less than 0.01). Shortening velocity was also depressed in SHR-F (0.95 +/- 0.38 lengths/s) compared with SHR-NF (1.60 +/- 0.30; P less than 0.05) and WKY groups (2.15 %/- 0.48; P less than 0.01). Depression of muscle function was not found before 18 mo of age. Thus the aging SHR is a model in which one can observe the transition from chronic stable left ventricular hypertrophy to overt heart failure. Furthermore, left ventricular papillary muscles from SHRs with heart failure show evidence of significant contractile dysfunction, suggesting that impairment of intrinsic myocardial function underlies the development of heart failure.

Preload does not affect relaxation rate in normal, hypoxic, or hypertrophic myocardium

To determine whether isolated changes in preload (end-diastolic force) can influence myocardial relaxation rate in normal or abnormal (hypoxic or hypertrophic) hearts, isolated LV papillary muscles from normal Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats were studied using physiologically sequenced contractions. While total (systolic) load and late (lengthening) load were held constant, maximum isometric force decline (peak -dT/dt) and maximum isotonic lengthening rate (peak +dL/dt) were measured at seven levels of preload that varied from 115 to 55% of the resting tension at maximum length-tension curves (Lmax). Muscles from normal rats were studied in the oxygenated state (95% O2-5% CO2) and in the hypoxic state (95% N2-5% CO2). Preload did not effect peak -dT/dt or peak +dL/dt in either oxygenated or hypoxic muscles. During hypoxia, peak -dT/dt and peak +dL/dt were 9.5 +/- 1.0 g.mm-2.s-1 and 0.3 +/- 0.1 muscle length/s, respectively, at a preload of 115% compared with 9.0 +/- 1.2 g.mm-2.s-1 and 0.2 +/- 0.1 at a preload of 55%. In separate experiments, the effect of preload on relaxation rate was studied in WKY and SHR rats. In neither group did preload have an independent effect on relaxation rate. In the SHRs, peak -dT/dt and peak +dL/dt were 24.3 +/- 5.3 g.mm-2.s-1 and 0.7 +/- 0.1 muscle length/s, respectively, at a preload of 115% compared with 24.7 +/- 6.6 and 0.8 +/- 0.1 at a preload of 55%. Thus, in hypoxic and hypertrophic myocardium, as in normal muscle, an acute isolated change in preload did not influence the rate of force decline or muscle lengthening.

Mechanical determinants of maximum isotonic lengthening rate in rat left ventricular myocardium

The effects of changing loading conditions and inotropic state on maximum isotonic lengthening rate (+dL/dt, muscle lengths/sec) were examined in isolated rat myocardium. Physiologically sequenced contractions were studied in 18 left ventricular papillary muscle preparations (stimulation rate, 12/min). To study the effects of changing loading conditions, only one loading variable (preload, total load, or late load) was changed during each contraction, while the others were held constant. To study the effects of isoproterenol (10(-6) M) and temperature (28 vs. 33 degrees C) on maximum isotonic lengthening rate, preload and late load were held constant and +dL/dt was examined at a common total load. When preload was increased from 0.7 +/- 0.1 to 1.4 +/- 0.1 g/mm2, muscle length increased from 0.98 +/- 0.003 to 1.01 +/- 0.002 muscle lengths, the extent of shortening increased from 0.05 +/- 0.003 to 0.08 +/- 0.003 muscle lengths, but minimum length (0.93 +/- 0.01 muscle lengths) and +dL/dt (1.1 +/- 0.1 muscle lengths/sec) were unchanged. When total load was increased from 1.5 to 4.5 g/mm2, minimum length increased from 0.91 +/- 0.05 to 0.97 +/- 0.05 muscle lengths and +dL/dt fell from 1.4 +/- 0.1 to 0.5 +/- 0.1 muscle lengths/sec. Late load (the load borne by or applied to the muscle during isotonic lengthening) was altered by changing its magnitude (g/mm2) or time (milliseconds after stimulation) of application. As late load was increased from 1.4 +/- 0.02 to 2.1 +/- 0.3 g/mm2, +dL/dt increased from 1.3 +/- 0.2 to 2.1 +/- 0.3 muscle lengths/sec.(ABSTRACT TRUNCATED AT 250 WORDS)

Energy costs of below-knee prostheses using two types of suspension

The choice of suspension in below-knee prosthetics poses a problem for the clinician because cuff suspension weighs less than side-joint-thigh corset suspension but the latter offers more stability. The energy costs of one compared with the other is of prime consideration when dealing with the older person after an amputation. To determine the energy costs of cuff and side-joint-thigh corset suspension, 17 patients were selected for study. A sepcial prosthetic bucket was fabricated for each patient and designed so that the suspensions could be quickly and easily interchanged. Trials with each method of suspension were carried out before and after a training period, and the cardiorespiratory parameters were measured. After the training period all patients demonstrated less oxygen consumption, but the type of suspension did not affect energy costs.