The onset of rare earth metallosis begins with renal gadolinium-rich nanoparticles from magnetic resonance imaging contrast agent exposure.

The leitmotifs of magnetic resonance imaging (MRI) contrast agent-induced complications range from acute kidney injury, symptoms associated with gadolinium exposure (SAGE)/gadolinium deposition disease, potentially fatal gadolinium encephalopathy, and irreversible systemic fibrosis. Gadolinium is the active ingredient of these contrast agents, a non-physiologic lanthanide metal. The mechanisms of MRI contrast agent-induced diseases are unknown. Mice were treated with a MRI contrast agent. Human kidney tissues from contrast-naïve and MRI contrast agent-treated patients were obtained and analyzed. Kidneys (human and mouse) were assessed with transmission electron microscopy and scanning transmission electron microscopy with X-ray energy-dispersive spectroscopy. MRI contrast agent treatment resulted in unilamellar vesicles and mitochondriopathy in renal epithelium. Electron-dense intracellular precipitates and the outer rim of lipid droplets were rich in gadolinium and phosphorus. We conclude that MRI contrast agents are not physiologically inert. The long-term safety of these synthetic metal-ligand complexes, especially with repeated use, should be studied further.

Gadolinium Deposition Disease: A Case Report and the Prevalence of Enhanced MRI Procedures Within the Veterans Health Administration.

Background: Gadolinium (Gd) usage in the Veterans Health Administration is increasing and patients with renal disease are frequently exposed. Gd is not entirely eliminated within 24 hours after administration, which may pose long-term adverse effects. Case Presentation: A Vietnam-era veteran aged > 70 years presented for evaluation of Gd-based contrast agent-induced chronic multisymptom illness. In the course of his routine clinical care, he was exposed to repeated Gd-enhanced magnetic resonance imaging studies. After his second Gd-based contrast agent exposure, he noted rash, pain, headaches, and hoarseness. Years after the exposure to the contrast agents, he continued to have detectable Gd in urine and serum. Conclusions: Practitioners should be aware of long-term intracellular Gd retention (including the brain) as patients increasingly turn to consultants with concerns about Gd deposition disease. Data from patient advocates demonstrate that Gd is eliminated in intermediate and long phases, which may represent a multicompartment model. The commercialization of Gd use in imaging studies is outpacing the science addressing the long-term consequences of harboring this alien, toxic, nonphysiologic rare earth metal.

Dysnatremia in Gastrointestinal Disorders.

The primary solute of the milieu intérieur is sodium and accompanying anions. The solvent is water. The kidneys acutely regulate homeostasis in filtration, secretion, and resorption of electrolytes, non-electrolytes, and minerals while balancing water retention and clearance. The gastrointestinal absorptive and secretory functions enable food digestion and water absorption needed to sustain life. Gastrointestinal perturbations including vomiting and diarrhea can lead to significant volume and electrolyte losses, overwhelming the renal homeostatic compensatory mechanisms. Dysnatremia, potassium and acid-base disturbances can result from gastrointestinal pathophysiologic processes. Understanding the renal and gastrointestinal contributions to homeostatis are important for the clinical evaluation of perturbed volume disturbances.

Overlapping roles of NADPH oxidase 4 for diabetic and gadolinium-based contrast agent-induced systemic fibrosis.

Dozens of millions of people are exposed to gadolinium-based contrast agents annually for enhanced magnetic resonance imaging. Gadolinium-based contrast agents are known nephrotoxins and can trigger the potentially fatal condition of systemic fibrosis. Risk factors are practically entirely undefined. We examined the role of NADPH oxidase 4 (Nox4) in gadolinium-induced systemic disease. Age- and weight-matched mice were randomized to experimental diabetes (streptozotocin) and control groups followed by systemic gadolinium-based contrast agent treatment. Nox4-deficient mice were randomized to experimental diabetes and gadolinium-based contrast agent treatment. Skin fibrosis and cellular infiltration were apparent in both gadolinium-based contrast agent-treated and experimental diabetes groups. Similarly, both groups demonstrated renal pathologies with evidence of reactive oxygen species generation. Deletion of Nox4 abrogated both skin and renal pathology, whether from diabetes or gadolinium-based contrast agent treatment. These discoveries demonstrate the importance of Nox4 in gadolinium-based contrast agent- and diabetes-induced fibrosis.NEW & NOTEWORTHY A mouse model of gadolinium-based contrast agent- and diabetes-induced fibrosis was used to demonstrate the role of NADPH oxidase 4 (Nox4) in gadolinium-induced systemic disease. Using these models, we established the role of Nox4 as a mediator of reactive oxygen species generation and subsequent skin and kidney fibrosis. These novel findings have defined Nox-4-mediated mechanisms by which gadolinium-based contrast agents induce systemic diseases.

Rosuvastatin-Induced Rhabdomyolysis, Pancreatitis, Transaminitis, and Acute Kidney Injury.

Changing medications within a drug class requires considering the indication and dosage, possible adverse effects, and drug-drug interactions.

Gadolinium-Based Contrast Agent Use, Their Safety, and Practice Evolution.

Gadolinium-based contrast agents (GBCAs) have provided much needed image enhancement in magnetic resonance imaging (MRI) important in the advancement of disease diagnosis and treatment. The paramagnetic properties of ionized gadolinium have facilitated these advancements, but ionized gadolinium carries toxicity risk. GBCAs were formulated with organic chelates designed to reduce these toxicity risks from unbound gadolinium ions. They were preferred over iodinated contrast used in computed tomography and considered safe for use. As their use expanded, the development of new diseases associated with their use (including nephrogenic systemic fibrosis) has drawn more attention and ultimately caution with their clinical administration in those with impaired renal function. Use of GBCAs in those with preserved renal function was considered to be safe. However, in this new era with emerging clinical and experimental evidence of brain gadolinium deposition in those with repeated exposure, these safety assumptions are once again brought into question. This review article aims to add new perspectives in thinking about the role of GBCA in current clinical use. The new information begs for further discussion and consideration of the risk-benefit ratio of use of GBCAs.

Biomechanical Restoration Potential of Pentagalloyl Glucose after Arterial Extracellular Matrix Degeneration.

The objective of this study was to quantify pentagalloyl glucose (PGG) mediated biomechanical restoration of degenerated extracellular matrix (ECM). Planar biaxial tensile testing was performed for native (N), enzyme-treated (collagenase and elastase) (E), and PGG (P) treated porcine abdominal aorta specimens (n = 6 per group). An Ogden material model was fitted to the stress-strain data and finite element computational analyses of simulated native aorta and aneurysmal abdominal aorta were performed. The maximum tensile stress of the N group was higher than that in both E and P groups for both circumferential (43.78 ± 14.18 kPa vs. 10.03 ± 2.68 kPa vs. 13.85 ± 3.02 kPa; p = 0.0226) and longitudinal directions (33.89 ± 8.98 kPa vs. 9.04 ± 2.68 kPa vs. 14.69 ± 5.88 kPa; p = 0.0441). Tensile moduli in the circumferential direction was found to be in descending order as N > P > E (195.6 ± 58.72 kPa > 81.8 ± 22.76 kPa > 46.51 ± 15.04 kPa; p = 0.0314), whereas no significant differences were found in the longitudinal direction (p = 0.1607). PGG binds to the hydrophobic core of arterial tissues and the crosslinking of ECM fibers is one of the possible explanations for the recovery of biomechanical properties observed in this study. PGG is a beneficial polyphenol that can be potentially translated to clinical practice for preventing rupture of the aneurysmal arterial wall.

Development of a total atherosclerotic occlusion with cell-mediated calcium deposits in a rabbit femoral artery using tissue-engineering scaffolds.

This study sought to establish a chronic total occlusion (CTO) model with cell-mediated calcium deposits in rabbit femoral arteries. CTO is the most severe case in atherosclerosis and contains calcium deposits. Previous animal models of CTO do not mimic the gradual occlusion of arteries or have calcium in physiological form. In the present study we tested the strategy of placing tissue-engineering scaffolds preloaded with cells in arteries to develop a novel CTO model. Primary human osteoblasts (HOBs) were first cultured in vitro on polycaprolactone (PCL) scaffolds with 5 ng TGFß1 loading for 28 days for precalcification. The HOB-PCL construct was then implanted into a rabbit femoral artery for an additional 3, 10 or 28 days. At the time of sacrifice, angiograms and gross histology of arteries were captured to examine the occlusion of arteries. Fluorescent staining of calcium and EDS detection of calcium were used to evaluate the presence and distribution of calcium inside arteries. Rabbit femoral arteries were totally occluded over 28 days. Calcium was presented at CTO sites at 3, 10 and 28 days, with the day 10 specimens showing the maximum calcium. Chronic inflammatory response and recanalization were observed in day 28 CTO sites. A novel CTO model with cell-mediated calcium has been successfully established in a rabbit femoral artery. This model can be used to develop new devices and therapies to treat severe atherosclerotic occlusion.

CC chemokine receptor 5 deletion impairs macrophage activation and induces adverse remodeling following myocardial infarction.

Post-myocardial infarction (MI), chemokine homing of inflammatory cells into the injured left ventricle (LV) regulates ventricular remodeling, in part by stimulating the extracellular matrix response. The CC chemokine receptor 5 (CCR5) is a key chemokine receptor expressed on macrophages, and CCR5 ligands are highly upregulated post-MI. We hypothesized that deletion of CCR5 would attenuate adverse remodeling by decreasing inflammatory cell recruitment. Accordingly, we examined LV function, macrophage recruitment and activation, and collagen content in wild-type (WT, n = 25) and CCR5 null (n = 33) mice at 7 days post-MI. Both groups had similar infarct sizes (44 ± 2% in WT and 42 ± 2% in CCR5 null; P = 0.37). However, the LV remodeling index (end diastolic volume/LV mass) increased to a larger extent in CCR5 null (1.28 ± 0.08 µl/mg for CCR5 null and 1.02 ± 0.06 µl/mg for WT; P < 0.05). Although numbers of infiltrated macrophages were similar in WT and CCR5 null mice, CCR5-deficient macrophages isolated from the infarct zone displayed >50% decrease in gene expression levels of proinflammatory activation markers (interleukin-1ß, interleukin-6, and tumor necrosis factor-α), as well as anti-inflammatory activation markers (arginase 1, CD163, mannose receptor, and transforming growth factor-ß1) compared with WT (all P < 0.05). Concomitant with the reduced macrophage activation, heat shock protein-47 and collagen type I precursor levels in the infarct region decreased in the CCR5 null (1.2 ± 0.3 units in the CCR5 null and 2.3 ± 0.4 units in the WT; P < 0.05), while collagen fragments increased (88.3 ± 5.9 units in the CCR5 null and 32.7 ± 8.5 units in the WT; P < 0.05). We conclude that CCR5 deletion impairs LV remodeling by hindering macrophage activation, which stimulates an imbalance in collagen metabolism and increases the remodeling index.

Caspase inhibition modulates left ventricular remodeling following myocardial infarction through cellular and extracellular mechanisms.

BACKGROUND: Myocyte death occurs by necrosis and caspase-mediated apoptosis in myocardial infarction (MI). In vitro studies suggest caspase activation causes myocardial contractile protein degradation without inducing apoptosis. Thus, caspase activation may evoke left ventricular (LV) remodeling through independent processes post-MI. The effects of caspase activation on LV geometry post-MI remain unclear. This project applied pharmacologic caspase inhibition (CASPI) to a porcine model of MI. METHODS AND RESULTS: Pigs (34 kg) were instrumented to induce 60 minutes of coronary artery occlusion followed by reperfusion and a 7-day follow-up period. Upon reperfusion, the pigs were randomized to saline (n = 12) or CASPI (n = 10, IDN6734, 6 mg/kg i.v., then 6 mg/kg/h for 24 hours). Plasma troponin-I values were reduced with CASPI compared with saline at 24 hours post-MI (133 +/- 15 vs. 189 +/- 20 ng/mL, respectively, P < 0.05). LV end-diastolic area (echocardiography) and interregional length (sonomicrometry) increased from baseline in both groups but were attenuated with CASPI by 40% and 90%, respectively (P < 0.05). Myocyte length was reduced with CASPI compared with saline (128 +/- 3 vs. 141 +/- 4 microm, respectively, P < 0.05). Plasma-free pro-matrix metalloproteinase-2 values increased from baseline with CASPI (27% +/- 6%, P < 0.05) indicative of reduced conversion to active MMP-2. Separate in vitro studies demonstrated that activated caspase species cleaved pro-MMP-2 yielding active MMP-2 forms and that MMP activity was increased in the presence of activated caspase-3. CONCLUSIONS: CASPI attenuated regional and global LV remodeling post-MI and altered viable myocyte geometry. Caspases increased MMP activity in vitro, whereas CASPI modified conversion of MMP-2 to the active form in vivo. Taken together, the results of the present study suggest that the elaboration of caspases post-MI likely contribute to LV remodeling through both cellular and extracellular mechanisms.

Cardiac-restricted overexpression of membrane type-1 matrix metalloproteinase in mice: effects on myocardial remodeling with aging.

BACKGROUND: The direct consequences of a persistently increased myocardial expression of the unique matrix metalloproteinase (MMP) membrane type-1 (MT1-MMP) on myocardial remodeling remained unexplored. METHODS AND RESULTS: Cardiac-restricted MT1-MMPexp was constructed in mice using the full-length human MT1-MMP gene ligated to the myosin heavy chain promoter, which yielded approximately a 200% increase in MT1-MMP when compared with age/strain-matched wild-type (WT) mice. Left ventricular (LV) function and geometry was assessed by echocardiography in 3-month ("young") WT (n=32) and MT1-MMPexp (n=20) mice and compared with 14-month ("middle-aged") WT (n=58) and MT1-MMPexp (n=35) mice. LV end-diastolic volume was similar between the WT and MT1-MMPexp young groups, as was LV ejection fraction. In the middle-aged WT mice, LV end-diastolic volume and ejection fraction was similar to young WT mice. However, in the MT1-MMPexp middle-aged mice, LV end-diastolic volume was approximately 43% higher and LV ejection fraction 40% lower (both P<0.05). Moreover, in the middle-aged MT1-MMPexp mice, myocardial fibrillar collagen increased by nearly 2-fold and was associated with approximately 3-fold increase in the processing of the profibrotic molecule, latency-associated transforming growth factor binding protein. In a second study, 14-day survival after myocardial infarction was significantly lower in middle-aged MT1-MMPexp mice. CONCLUSIONS: Persistently increased myocardial MT1-MMP expression, in and of itself, caused LV remodeling, myocardial fibrosis, dysfunction, and reduced survival after myocardial injury. These findings suggest that MT1-MMP plays a mechanistic role in adverse remodeling within the myocardium.

The left ventricle proteome differentiates middle-aged and old left ventricles in mice.

Middle-aged and old left ventricles (LVs) are structurally and functionally very similar. Compared to a young LV, both show increased wall thickness and increased cavity size, with preserved cardiac function. However, when a stressor such as myocardial infarction occurs, striking differences are revealed between young and old LVs and there is a marked reduction in survival rates for the old group. The objective of this study was to investigate the proteomic basis of age-related changes in the LV of male mice in order to identify proteins that are differentially expressed between middle-aged and old groups and to gain mechanistic insight into effects of aging on the unstressed heart. Young (3 months old; n = 6), middle-aged (MA; 15 months old; n = 6), and old (23 months old; n = 5) LVs were examined by echocardiography, homogenized, and separated into soluble and insoluble protein fractions using differential extraction. We found that the LV mass-to-tibia ratio increased from 6.4 +/- 0.2 mg/mm in young to 11.0 +/- 0.6 and 10.1 +/- 0.7 mg/mm in MA and old, respectively (both p < 0.05 vs young), which was caused by increases in both LV wall thickness and volume. Using two-dimensional gel electrophoresis, we detected age-related alterations in the levels of 73 proteins (all p < 0.05). Among these proteins were mortalin, peroxiredoxin 3, epoxide hydrolase, and the superoxide dismutases SOD-1 (Cu/ZnSOD) and SOD-2 (MnSOD), which have been previously associated with aging and/or cardiovascular disease. Together, these results reveal proteomic changes that occur in the LV with age. The proteins identified here may be useful markers of cardiac aging and may help in deducing mechanisms to explain the inability of the old heart to withstand challenge.

Chronic matrix metalloproteinase inhibition following myocardial infarction in mice: differential effects on short and long-term survival.

Left ventricular (LV) remodeling occurs after myocardial infarction (MI), and the matrix metalloproteinases (MMPs) contribute to adverse LV remodeling after MI. Short-term pharmacological MMP inhibition (MMPi; days to weeks) in animal models of MI have demonstrated a reduction in adverse LV remodeling. However, the long-term effects (months) of MMPi on survival and LV remodeling after MI have not been examined. MI was induced in adult mice (n = 131) and, at 3 days post-MI, assigned to MMPi [MI-MMPi: (s)-2-(4-bromo-biphenyl-4-sulfonylamino)-3-methyl-butyric acid (PD200126), 7.5 mg/day/p.o., n = 64] or untreated (MI-only, n = 67). Unoperated mice (n = 16) served as controls. The median survival in the MI-only group was 5 days, whereas median survival was significantly greater in the MI-MMPi group at 38 days (p < 0.05). However, with prolonged MMPi (>120 days), a significant divergence in the survival curves occurred in which significantly greater mortality was observed with prolonged MMPi (p < 0.05). LV echocardiography at 6 months revealed LV dilation in the MI-only and MI-MMPi groups (154 +/- 14 and 219 +/- 24 microl) compared with control (67 +/- 4 microl, p < 0.05), with a greater degree of dilation in the MI-MMPi group (p < 0.05). MMPi conferred a beneficial effect on survival early post-MI, but prolonged MMPi (>3 months) was associated with higher mortality and adverse LV remodeling. These unique results suggest that an optimal temporal window exists with respect to pharmacological interruption of MMP activity in the post-MI period.

Selective spatiotemporal induction of matrix metalloproteinase-2 and matrix metalloproteinase-9 transcription after myocardial infarction.

Myocardial remodeling after myocardial infarction (MI) is associated with increased levels of the matrix metalloproteinases (MMPs). Levels of two MMP species, MMP-2 and MMP-9, are increased after MI, and transgenic deletion of these MMPs attenuates post-MI left ventricular (LV) remodeling. This study characterized the spatiotemporal patterns of gene promoter induction for MMP-2 and MMP-9 after MI. MI was induced in transgenic mice in which the MMP-2 or MMP-9 promoter sequence was fused to the beta-galactosidase reporter, and reporter level was assayed up to 28 days after MI. Myocardial localization with respect to cellular sources of MMP-2 and MMP-9 promoter induction was examined. After MI, LV diameter increased by 70% (P < 0.05), consistent with LV remodeling. beta-Galactosidase staining in MMP-2 reporter mice was increased by 1 day after MI and increased further to 64 +/- 6% of LV epicardial area by 7 days after MI (P < 0.05). MMP-2 promoter activation occurred in fibroblasts and myofibroblasts in the MI region. In MMP-9 reporter mice, promoter induction was detected after 3 days and peaked at 7 days after MI (53 +/- 6%, P < 0.05) and was colocalized with inflammatory cells at the peri-infarct region. Although MMP-2 promoter activation was similarly distributed in the MI and border regions, activation of the MMP-9 promoter was highest at the border between the MI and remote regions. These unique findings visually demonstrated that activation of the MMP-2 and MMP-9 gene promoters occurs in a distinct spatial relation with reference to the MI region and changes in a characteristic time-dependent manner after MI.

Matrix metalloproteinase-7 affects connexin-43 levels, electrical conduction, and survival after myocardial infarction.

BACKGROUND: Matrix metalloproteinases (MMPs) contribute to left ventricular remodeling after myocardial infarction (MI). Specific causative roles of particular MMPs, however, remain unclear. MMP-7 is abundant in cardiomyocytes and macrophages, but MMP-7 function after MI has not been defined. METHODS AND RESULTS: Wild-type (WT; n=55) and MMP-7-null (MMP-7-/-; n=32) mice underwent permanent coronary artery ligation for 7 days. MI sizes were similar, but survival was greatly improved in MMP-7-/- mice. The survival difference could not be attributed to differences in left ventricular dilation because end-diastolic volumes increased similarly. ECG analysis revealed a prolonged PR interval in WT but not in MMP-7-/- post-MI mice. Post-MI conduction velocity, determined by optically mapping electrical wavefront propagation, decreased to 78+/-6% of control for WT and was normalized in MMP-7-/- mice. In WT mice, slower conduction velocity correlated with a 53% reduction in the gap junction protein connexin-43. Direct binding of MMP-7 to connexin-43, determined by surface plasmon resonance technology, occurred in a dose-dependent manner. Connexin-43 processing by MMP-7 was confirmed by in silico and in vitro substrate analyses and MMP-7 infusion induced arrhythmias in vivo. CONCLUSIONS: MMP-7 deletion results in improved survival and myocardial conduction patterns after MI. This is the first report to implicate MMP-7 in post-MI remodeling and to demonstrate that connexin-43 is a novel MMP-7 substrate.

Matrix metalloproteinase-9 gene deletion facilitates angiogenesis after myocardial infarction.

Matrix metalloproteinases (MMPs) are postulated to be necessary for neovascularization during wound healing. MMP-9 deletion alters remodeling postmyocardial infarction (post-MI), but whether and to what degree MMP-9 affects neovascularization post-MI is unknown. Neovascularization was evaluated in wild-type (WT; n = 63) and MMP-9 null (n = 55) mice at 7-days post-MI. Despite similar infarct sizes, MMP-9 deletion improved left ventricular function as evaluated by hemodynamic analysis. Blood vessel quantity and quality were evaluated by three independent studies. First, vessel density was increased in the infarct of MMP-9 null mice compared with WT, as quantified by Griffonia (Bandeiraea) simplicifolia lectin I (GSL-I) immunohistochemistry. Second, preexisting vessels, stained in vivo with FITC-labeled GSL-I pre-MI, were present in the viable but not MI region. Third, a technetium-99m-labeled peptide (NC100692), which selectively binds to activated alpha(v)beta3-integrin in angiogenic vessels, was injected into post-MI mice. Relative NC100692 activity in myocardial segments with diminished perfusion (0-40% nonischemic) was higher in MMP-9 null than in WT mice (383 +/- 162% vs. 250 +/- 118%, respectively; P = 0.002). The unique finding of this study was that MMP-9 deletion stimulated, rather than impaired, neovascularization in remodeling myocardium. Thus targeted strategies to inhibit MMP-9 early post-MI will likely not impair the angiogenic response.

Altered fibroblast function following myocardial infarction.

Adequate wound healing and scar formation is an essential response to myocardial infarction (MI), and fibroblasts are primary cellular components regulating the process. How fibroblast functions are altered post-MI and to what extent these abnormalities persist in vitro is not well understood. Accordingly, we isolated myocardial fibroblasts from MI and non-MI (remote) regions at 7 days post-MI (n=35) and from the free wall and septum of unoperated control C57BL/6 mice (n=14). Proliferation was increased 182+/-28% in MI, but not in remote, fibroblasts compared with unoperated controls (P=0.01). Migration decreased 61+/-8%, adhesion to laminin decreased 79+/-8%, adhesion to collagen IV increased 196+/-27%, and collagen synthesis increased 169+/-24% in fibroblasts isolated from the MI region (all P<0.05). Migration, adhesion, and collagen synthesis changes were similar in remote fibroblasts, and the phenotypic differences were maintained through passage four. Transforming growth factor beta1 (TGFbeta1) is a bioactive molecule that has been shown to affect fibroblast function. Stimulation of unoperated control fibroblasts with 10 ng/ml TGFbeta(1) increased proliferation 137+/-7% (P=0.03 vs. unstimulated), increased adhesion to collagen IV 149+/-6% (P<0.01), and increased collagen I levels 187+/-10% (P=0.01). TGFbeta1 may, therefore, explain some of the changes in post-MI fibroblast phenotype. These data demonstrate for the first time region specific alterations in post-MI fibroblast biology that are maintained in vitro. Additionally, our model provides a novel in vitro template for examining the cellular mechanisms of wound healing and scar formation post-MI.

Age-dependent changes in myocardial matrix metalloproteinase/tissue inhibitor of metalloproteinase profiles and fibroblast function.

OBJECTIVE: To evaluate the effects of aging on left ventricular (LV) geometry, collagen levels, matrix metalloproteinase (MMP) and tissue inhibitor of metalloproteinase (TIMP) abundance, and myocardial fibroblast function. METHODS: Young (3-month-old; n=28), middle-aged (MA; 15-month-old; n=17), and old (23-month-old; n=16) CB6F1 mice of both sexes were used in this study. Echocardiographic parameters were measured; collagen, MMP, and TIMP levels were determined for both the soluble and insoluble protein fractions; and fibroblast function was evaluated. RESULTS: LV end-diastolic dimensions and wall thickness increased in both MA and old mice, accompanied by increased soluble protein and decreased insoluble collagen. Immunoblotting revealed differential MMP/TIMP profiles. Compared to MA levels, MMP-3, MMP-8, MMP-9, MMP-12, and MMP-14 increased, and TIMP-3 and TIMP-4 decreased in the insoluble fraction of old mice, suggesting increased extracellular matrix (ECM) degradative capacity. Fibroblast proliferation was blunted with age. CONCLUSION: This study, for the first time, identified specific differences in cellular and extracellular processes that likely contribute to age-dependent ECM remodeling.

Myocardial remodeling after discrete radiofrequency injury: effects of tissue inhibitor of matrix metalloproteinase-1 gene deletion.

Discrete myocardial lesions created through the delivery of radiofrequency (RF) energy can expand; however, the mechanisms have not been established. Matrix metalloproteinases (MMPs) play an important role in myocardial remodeling, and MMP activity can be regulated by the tissue inhibitors of the metalloproteinases (TIMPs). This study examined the role of TIMP-1 in postinjury myocardial remodeling. Lesions were created on the left ventricular (LV) epicardium of wild-type (WT, 8-12 wk, 129SVE) and age-matched TIMP-1 gene-deficient (timp-1(-/-)) mice through the delivery of RF current (80 degrees C, 30 s). Heart mass, LV scar volumes, and collagen content were measured at 1 h and 3, 7, and 28 days postinjury (n = 10 each). Age-matched, nonablated mice were used as reference controls (n = 5). Heart mass indexed to tibial length increased in WT and timp-1(-/-) mice but was greater in the timp-1(-/-) mice by 7 days. Scar volumes increased in a time-dependent manner in both groups but were higher in the timp-1(-/-) mice than the WT mice at 7 days (1.48 +/- 0.09 vs. 1.20 +/- 0.11 mm(3).mg(-1).mm, P < 0.05) and remained higher at 28 days. In the remote myocardium, wall thickness was greater and relative collagen content was lower in the timp-1(-/-) mice at 28 days postinjury. Discrete myocardial RF lesions expand in a time-dependent manner associated with myocyte hypertrophy remote to the scar. Moreover, postinjury myocardial remodeling was more extensive with TIMP-1 gene deletion. Thus TIMP-1 either directly or through modulation of MMP activity may regulate myocardial remodeling following infliction of a discrete injury.

Pharmacologic inhibition of intracellular caspases after myocardial infarction attenuates left ventricular remodeling: a potentially novel pathway.

OBJECTIVE: Myocyte death occurs by necrosis and caspase-mediated apoptosis in the setting of myocardial infarction. In vitro studies suggest that caspase activation within myocytes causes contractile protein degradation without inducing cell death. Thus, caspase activation may evoke left ventricular remodeling through 2 independent processes post-myocardial infarction. However, the effects of caspase activation on left ventricular geometry post-myocardial infarction remain unclear. This project applied broad-spectrum caspase inhibition to a chronic porcine model of myocardial infarction. METHODS: Coronary snares and sonomicrometry crystals in remote and area-at-risk regions were placed in pigs (n = 22, 34 kg). Geometric measurements at end diastole and end systole, including left ventricular area by echocardiography and interregional distance by sonomicrometry, were obtained at baseline. Coronary occlusion was instituted for 60 minutes, followed by reperfusion and repeated geometric measurements at 7 days, including left ventriculography. At reperfusion, pigs were randomized to saline (n = 12) or caspase inhibition (n = 10, IDN6734, 2 mg/kg intravenously, then 2 mg x kg x h for 24 hours) at a dose that achieved desired plasma concentrations (790 +/- 142 ng/mL) as predicted by prior pharmacokinetic studies. RESULTS: Infarct size and 24-hour troponin-I values were not significantly different between the saline and caspase inhibition groups (51% +/- 8% vs 42% +/- 6% and 189 +/- 20 ng/mL vs 152 +/- 26 ng/mL, respectively, P >.10). At 7 days, end-diastole volume was increased in both groups compared with reference control values (47 +/- 1 mL, P <.05), but it was decreased with caspase inhibition (72 +/- 4 mL) compared with saline (84 +/- 4 mL, P <.05). Similarly, end-diastole and end-systole areas increased by 32% +/- 3% and 81% +/- 16% in the saline group but were attenuated with caspase inhibition (19% +/- 3% and 31% +/- 10%, respectively, P <.05). End-diastole interregional distance increased by 30% +/- 7% in the saline group but was attenuated with caspase inhibition (12% +/- 5%, P <.05). CONCLUSION: Despite equivalent degrees of myocardial injury, caspase inhibition reduced post-myocardial infarction left ventricular remodeling as evidenced by multiple, independent assessments of left ventricular dilation. Thus, caspase activation alters left ventricular geometry in the absence of significant effects on myocardial injury.