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Articles by J Robbins
Total Records ( 3 ) for J Robbins
  S. L Gray , A. Z LaCroix , J Larson , J Robbins , J. A Cauley , J. E Manson and Z. Chen

Background  Proton pump inhibitor (PPI) medications have been inconsistently shown to be associated with osteoporotic fractures. We examined the association of PPI use with bone outcomes (fracture, bone mineral density [BMD]).

Methods  This prospective analysis included 161 806 postmenopausal women 50 to 79 years old, without history of hip fracture, enrolled in the Women's Health Initiative (WHI) Observational Study and Clinical Trials with a mean (SD) follow-up of 7.8 (1.6) years. Analyses were conducted for 130 487 women with complete information. Medication information was taken directly from drug containers during in-person interviews (baseline, year 3). The main outcome measures were self-reported fractures (hip [adjudicated], clinical spine, forearm or wrist, and total fractures) and for a subsample (3 densitometry sites), 3-year change in BMD.

Results  During 1 005 126 person-years of follow-up, 1500 hip fractures, 4881 forearm or wrist fractures, 2315 clinical spine fractures, and 21 247 total fractures occurred. The multivariate-adjusted hazard ratios for current PPI use were 1.00 (95% confidence interval [CI], 0.71-1.40) for hip fracture, 1.47 (95% CI, 1.18-1.82) for clinical spine fracture, 1.26 (95% CI, 1.05-1.51) for forearm or wrist fracture, and 1.25 (95% CI, 1.15-1.36) for total fractures. The BMD measurements did not vary between PPI users and nonusers at baseline. Use of PPIs was associated with only a marginal effect on 3-year BMD change at the hip (P = .05) but not at other sites.

Conclusion  Use of PPIs was not associated with hip fractures but was modestly associated with clinical spine, forearm or wrist, and total fractures.

  F. L Xiang , X Lu , L Hammoud , P Zhu , P Chidiac , J Robbins and Q. Feng

Background— Soluble stem cell factor (SCF) has been shown to mobilize bone marrow stem cells and improve cardiac repair after myocardial infarction (MI). However, the effect of membrane-associated SCF on cardiac remodeling after MI is not known. The present study investigated the effects of cardiomyocyte-specific overexpression of the membrane-associated isoform of human SCF (hSCF) on cardiac function after MI.

Methods and Results— A novel mouse model with tetracycline-inducible and cardiac-specific overexpression of membrane-associated hSCF was generated. MI was induced by left coronary artery ligation. Thirty-day mortality after MI was decreased in hSCF/tetracycline transactivator (tTA) compared with wild-type mice. In vivo cardiac function was significantly improved in hSCF/tTA mice at 5 and 30 days after MI compared with wild-type mice. Endothelial progenitor cell recruitment and capillary density were increased and myocardial apoptosis was decreased in the peri-infarct area of hSCF/tTA mice. Myocyte size was decreased in hSCF/tTA mice 30 days after MI compared with WT mice. Furthermore, hSCF overexpression promoted de novo angiogenesis as assessed by matrigel implantation into the left ventricular myocardium.

Conclusions— Cardiomyocyte-specific overexpression of hSCF improves myocardial function and survival after MI. These beneficial effects of hSCF may result from increases in endothelial progenitor cell recruitment and neovascularization and decreases in myocardial apoptosis and cardiac remodeling.

  T Suzuki , B. M Palmer , J James , Y Wang , Z Chen , P VanBuren , D. W Maughan , J Robbins and M. M. LeWinter

Background— The left ventricles of both rabbits and humans express predominantly β-myosin heavy chain (MHC). Transgenic (TG) rabbits expressing 40% -MHC are protected against tachycardia-induced cardiomyopathy, but the normal amount of -MHC expressed in humans is only 5% to 7% and its functional importance is questionable. This study was undertaken to identify a myofilament-based mechanism underlying tachycardia-induced cardiomyopathy protection and to extrapolate the impact of MHC isoform variation on myofilament function in human hearts.

Methods and Results— Papillary muscle strips from TG rabbits expressing 40% (TG40) and 15% -MHC (TG15) and from nontransgenic (NTG) controls expressing 100% β-MHC (NTG40 and NTG15) were demembranated and calcium activated. Myofilament tension and calcium sensitivity were similar in TGs and respective NTGs. Force-clamp measurements revealed 50% higher power production in TG40 versus NTG40 (P<0.001) and 20% higher power in TG15 versus NTG15 (P<0.05). A characteristic of acto-myosin crossbridge kinetics, the "dip" frequency, was significantly higher in TG40 versus NTG40 (0.70±0.04 versus 0.39±0.09 Hz, P<0.01) but not in TG15 versus NTG15. The calculated crossbridge time-on was also significantly shorter in TG40 (102.3±14.2 ms) versus NTG40 (175.7±19.7 ms) but not in TG15 versus NTG15.

Conclusions— The incorporation of 40% -MHC leads to greater myofilament power production and more rapid crossbridge cycling, which facilitate ejection and relengthening during short cycle intervals, and thus protect against tachycardia-induced cardiomyopathy. Our results suggest, however, that, even when compared with the virtual absence of -MHC in the failing heart, the 5% to 7% -MHC content of the normal human heart has little if any functional significance.

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