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Diaphragm adaptations following treatment for emphysema

Institution: Cedars-Sinai Medical Center
Investigator(s): Michael Lewis, M.D.
Award Cycle: 1997 (Cycle 6) Grant #: 6RT-0144 Award: $469,400
Subject Area: Pulmonary Disease
Award Type: Research Project Awards
Abstracts

Initial Award Abstract
Cigarette smoking is the most important risk factor for the development of emphysema. With emphysema, the lungs become overinflated and this severely impairs the function of the diaphragm, the most important of the breathing muscles. During this disease progression, the diaphragm muscle adapts in an attempt to preserve its ability to sustain work capacity. In particular, the actual length of diaphragm muscle fibers become absolutely shorter. Lung volume reduction surgery (LVRS) is a new procedure for patients with severe emphysema who, despite the best medical therapy available and pulmonary rehabilitation programs, continue to have disabling shortness of breath and very poor quality of life. The procedure involves removing about a third of the most diseased portions of each lung. With the reduction in volume of the overinflated lungs, the shape and function of the diaphragm would be expected to be altered following this procedure. There are, however, no studies which characterize the functional, cellular, and biochemical adaptations occurring in the diaphragm muscle following this procedure.

Detailed examination of the diaphragm muscle structure and function is not feasible in patients undergoing this procedure, as it would be prohibitively invasive and unethical. We therefore elected to examine diaphragm per-formance following LVRS in a hamster model of emphysema. We believe that these studies are important because we hypothesize that in the immediate post-operative phase following LVRS, a variety of factors may act on the stretched but anatomically shortened diaphragm muscle, to temporarily injure it and thus impair its performance. We hypothesize, however, that in the long-term, partial or complete remodeling of the diaphragm to a more normal state will ensue.

Six months following the development of emphysema, a group of animals will be subjected to LVRS. The emphysemic animals subjected to LVRS will be compared to both a control group in which emphysema was not induced and an emphysema group. In both the control and emphysema only groups, sham surgery will be performed. Detailed studies on diaphragm structure and function will be performed two days following LVRS (the acute phase) and one at three months following LVRS (the chronic phase) in separate animals. A variety of sophisticated tests will be performed to assess the function of the diaphragm and its ability to generate force as well as indices of injury of the individual diaphragm muscle fibers. In addition, the long-term adaptations of the diaphragm during the chronic phase will be assessed using a variety of studies in a tissue bath to assess the function of the diaphragm as well as sophisticated tests to evaluate cellular, biochemical, and molecular adaptations.

This approach will allow us to test meaning-ful hypotheses with strong clinical implications that would not be possible in the human subject. Results from the acute phase may have important clinical implications for patients during the potentially vulnerable perioperative period. Likewise, data in the chronic phase will highlight the functional and cellular changes that occur in the diaphragm, which would have important inferences for the long-term rehabilitation of humans undergoing LVRS.

Final Report
The major objective of this proposal is to characterize the physiologic, cellular and biochemical mechanisms underlying the potential improvement in diaphragm performance following lung volume reduction surgery (LVRS) in an animal model of emphysema. LVRS involves the surgical removal of about 1/3 of each lung The hypotheses to be tested are: 1) Acute postoperative phase: Rapid re-establishment of a more normal chest configuration and a reduced lung volume will temporarily impair diaphragm force generating capacity in response to the stretch imposed on the anatomically shortened diaphragm muscle. 2) Chronic phase: The long term adaptations of the diaphragm muscle to LVRS in the emphysematous hamster will result in partial or complete re-establishment of the structural, functional and cellular properties of the diaphragm.

Major efforts were made to re-validate the emphysema model in hamsters at varying time points. Our efforts resulted in a reproducible model of lung over-inflation, as noted in patients with emphysema, with maximum lung volumes about 180% compared to those of control animals. Our surgical technique for bilateral LVRS was also modified in a way that mimics the procedures used in patients with good short- and long-terms results. As in patients about 30% of each lung was resected with a corresponding reduction in maximum lung volume. With this reduction in lung volume we postulated that the diaphragm muscle would be acutely stretched. Using specially implanted crystals we have demonstrated acute stretch of the diaphragm immediately following LVRS. We further postulated that breathing efforts in these circumstances could result in injury to diaphragm muscle fibers. We have demonstrated rupture of the membrane (sarcolemma) of a significant proportion of diaphragm muscle fibers using a fluorescent dye technique after 1 and 4 days following LVRS. Sarcolemmal rupture was greatest after 1 day with probable resealing after 4 days. The proportion of membrane rupture increased with greater degrees of resection. Electron microscopic studies to identify ultrastructural injury within individual diaphragm muscle fibers showed significant injury 1 day following LVRS with more extensive changes after 4 days. We postulated that stretch-induced injury may be a necessary signal for adaptive remodeling of diaphragm muscle fibers as the thorax adapts to a lower total lung volume. Insulin-like growth factor-1 (IGF-1) is an important polypeptide growth factor, which we postulate plays an important role in the process of muscle repair and remodeling following injury. Assays for diaphragm IGF-1 1 and 4 days after LVRS or sham surgery revealed a significant increase in IGF-1 protein in the diaphragm 4 days following LVRS. The changes in IGF-1 appeared greatest in those fibers demonstrating the greatest injury. Long-term adaptations of the diaphragm to LVRS were assessed 5 to 6 weeks after surgery. There was a tendency for the optimal length of diaphragm fibers to increase as well as for the generation of a higher degree of force production by the muscle. LVRS did not affect the speed-related properties of muscle contraction or the fatigability of the diaphragm. The proportions of myosin heavy chain isoforms (the most important muscle contractile proteins) were not affected following LVRS.

Our results suggest that in the acute postoperative phase following LVRS, the acutely stretched diaphragm is susceptible to injury, which in the presence of added loads may be excessive and complicate and delay functional recovery from the surgery. The results also highlight the potential for rapid cellular repair and remodeling to accommodate the new geometric chest configuration and mechanics imposed by the surgery. Our results provide important insights for the clinical condition in which such studies would not be feasible.
Publications

Role of muscle IGF-1 system in mediating the anabolic effects of nandrolone
Periodical: Society for Neuroscience Abstracts Index Medicus:
Authors: Fournier M, Clemmons DR, Lewis MI ABS
Yr: 1998 Vol: 24 Nbr: Abs: 1674 Pg:

Alterations in diaphragm contractility after nandrolone administration: an analysis of potential mechanisms
Periodical: Journal of Applied Physiology Index Medicus:
Authors: Lewis MI, Fournier M, Yeh AY, Micevych PE, Sieck GC ART
Yr: 1999 Vol: 86 Nbr: Abs: Pg: 985-992

IGF-1 administration prevents corticosteroid-induced diaphagm atrophy in emphysematous hamsters
Periodical: American Journal of Respiratory and Critical Care Medicine Index Medicus:
Authors: Lewis MI, Bulut Y, Biring MS, Da X, Fournier M ABS
Yr: 1999 Vol: 159 Nbr: Abs: A580 Pg:

Role of muscle IGF-1 system in modulating the effects of nandrolone
Periodical: American Journal of Respiratory and Critical Care Medicine Index Medicus:
Authors: Fournier M, Horvitz GD, Clemmons DR, Lewis MI ABS
Yr: 1999 Vol: 159 Nbr: Abs: A580 Pg:

Influences of corticosteroids on diaphragm muscle IGF-1 and ubiquitin-conjugating enzyme E2-14k
Periodical: American Journal of Respiratory and Critical Care Medicine Index Medicus:
Authors: Fournier M, Huang Z-S, Lewis MI ART
Yr: 2000 Vol: 161 Nbr: Abs: Pg: A119

Administration of insulin-like growth factor-1 (IGF-1) and corticosteroids in emphysematous hamsters: influences on diaphragm IGF-1
Periodical: American Journal of Respiratory and Critical Care Medicine Index Medicus:
Authors: Fournier M, Huang Z-S, Cercek B, Li H, Bykhovskaya I, Lewis MI ART
Yr: 2000 Vol: 161 Nbr: Abs: Pg: A18

Early cellular responses in diaphragm fibers of emphysematous hamsters following lung volume reduction surgery (LVRS)
Periodical: American Journal of Respiratory and Critical Care Medicine Index Medicus:
Authors: Lew MI, Da X, Mohsenifar Z, Fournier M ABS
Yr: 2001 Vol: 163 Nbr: Abs: A286 Pg:

Diaphragm IGF-1 responses to lung volume reduction surgery (LVRS) in emphysematous hamsters
Periodical: American Journal of Respiratory and Critical Care Medicine Index Medicus:
Authors: Fournier M, Li H, Da X, Mohsenifar Z, Lewis MI ABS
Yr: 2001 Vol: 163 Nbr: Abs: A147 Pg:

Diaphragm IGF-1 responses to nandrolone in malnourished emphysematous hamsters
Periodical: American Journal of Respiratory and Critical Care Medicine Index Medicus:
Authors: Fournier M, Li H, Da X, Biring MS, Lewis MI ABS
Yr: 2001 Vol: 163 Nbr: Abs: A147 Pg: