HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:
Guest Access | Sign In via User Name/Password

This Article Abstract Full Text (PDF) Free Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Add to My Personal Article Archive Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (4) Citing Articles via Google Scholar Google Scholar Articles by Cantor, J. O. Articles by Turino, G. M. Search for Related Content PubMed PubMed Citation Articles by Cantor, J. O. Articles by Turino, G. M.

Can Exogenously Administered Hyaluronan Improve Respiratory Function in Patients With Pulmonary Emphysema?^*

^* From St. John’s University (Dr. Cantor); and St. Luke’s-Roosevelt Hospital Center (Dr. Turino), New York, NY.

Correspondence to: Jerome Cantor, MD, College of Pharmacy and Allied Health Professions, St. John’s University, 8000 Utopia Pkwy, Jamaica, NY 11439; e-mail: JOCANTOR{at}pol.net

	Abstract

TOP Abstract Introduction Experimental Findings Proposed Role of Nebulized... The Potential Effect of... Conclusions References

 
While most attempts at developing a treatment for pulmonary emphysema have focused on the use of elastase inhibitors to reduce elastic fiber damage and the loss of alveoli, this laboratory has developed a method of preventing such injury by the intratracheal administration of hyaluronan (HA). Animals treated with HA prior to the induction of experimental emphysema develop significantly less disease than untreated controls. The protective effect of HA may be related to its ability to bind to lung elastic fibers, thereby preventing their breakdown by elastases. Although clinical trials involving nebulized HA are not expected to yield a measurable treatment effect for at least several years, it is proposed that the special ability of this polysaccharide to retain water may increase the elasticity of lung elastic fibers, producing a relatively rapid improvement in pulmonary mechanics. Such an outcome might speed the development of this potential treatment for pulmonary emphysema.

Key Words: elastase • elastic fibers • emphysema • hyaluronan

	Introduction

TOP Abstract Introduction Experimental Findings Proposed Role of Nebulized... The Potential Effect of... Conclusions References

 
The lack of an effective form of treatment for pulmonary emphysema reflects the difficulty of controlling a progressively destructive disease involving a complex organ such as the lung. In terms of understanding the basic disease mechanism, the use of the enzyme papain to experimentally induce emphysema represented an initial breakthrough.¹ Originally intended as a possible treatment for interstitial pulmonary fibrosis, the intratracheal instillment of papain produced prominent pulmonary airspace enlargement, which was similar to that seen in human emphysema. The finding had added significance because it came at a time when the role of ₁-antiproteinase deficiency in this disease was just being understood.² Both observations emphasized the importance of proteolysis as a cause of pulmonary emphysema. An imbalance between lung proteases and their inhibitors was hypothesized to be responsible for the airspace enlargement that characterizes the disease.^{3 4} It was proposed that an excess of elastase activity in the pulmonary parenchyma caused damage to the elastic fiber network of the lung, leading to dilatation and rupture of alveoli, reduced gas exchange, and eventual respiratory failure.

The proteinase-antiproteinase concept of emphysema served to focus research on the role of elastases with the hope that inhibiting the activity of these enzymes would prevent lung injury. This treatment strategy assumes, however, that emphysema is caused by a single abnormality, namely, excess elastase activity. If the disease represents a more general response of the lung to a variety of insults (with elastases playing a variable role), then enzyme inhibition may have only limited efficacy.

An alternative approach to treating emphysema, currently under development in this laboratory, involves the use of aerosolized hyaluronan (HA) to directly protect lung elastic fibers from injury.^{5 6 7 8} HA, a long-chain polysaccharide, has been shown to preferentially bind to elastic fibers, to prevent elastolysis, and to limit airspace enlargement in experimental models of emphysema induced by either porcine pancreatic elastase or human neutrophil elastase.^{6 7 8} Since elastic fiber breakdown may be a final common pathway in pulmonary emphysema, this form of treatment might be effective against a number of agents capable of causing the disease, including various types of elastases and oxidants that are present in air pollutants and cigarette smoke.

As aerosolized HA enters clinical trials in the near future, it is presumed that a beneficial treatment effect may not become evident for at least several years. The delay is due to the fact that pulmonary emphysema progresses at a relatively slow rate and that the available methods for measuring loss of lung function are not particularly sensitive. This assumption is based, however, on previous trials^{9 10 11} with pulmonary drugs that act in a radically different manner than HA. Indeed, there is no existing paradigm for a treatment agent such as HA, the postulated mechanism of action of which involves modification of the extracellular environment.

The special ability of HA to retain relatively large amounts of water, previously demonstrated both in vitro and in vivo,^{12 13 14} may potentially produce a rapid improvement in pulmonary mechanics, leading to relief of symptoms associated with impaired ventilation. In addition to reducing the time frame for clinically testing this agent, such an outcome might suggest a new strategy for treating diseases involving injury to the extracellular matrix.

	Experimental Findings

TOP Abstract Introduction Experimental Findings Proposed Role of Nebulized... The Potential Effect of... Conclusions References

 
The conceptual basis for using nebulized HA to treat pulmonary emphysema developed from a series of animal experiments designed to determine whether agents other than elastases are capable of inducing or enhancing pulmonary emphysema. A nonelastolytic enzyme, hyaluronidase, was shown to produce pulmonary airspace enlargement in hamsters when administered in conjunction with 60% oxygen therapy.¹⁵ Damage to elastic fibers occurred only when both agents were given concomitantly, suggesting the possibility that hyaluronidase may facilitate the breakdown of these fibers by making them more accessible to injury. This hypothesis was also tested in studies demonstrating that intratracheally administered hyaluronidase enhances airspace enlargement in a well-established hamster model of emphysema induced by the intratracheal administration of elastase.⁵

Experiments then were undertaken to examine the effect of HA itself on this model of emphysema. Animals treated with an aerosol composed of 0.1% HA in water for 50 min, then instilled intratracheally with elastase immediately thereafter, had significantly less airspace enlargement than controls treated with aerosolized water and elastase (Fig 1 ).^{7 8} Studies using fluorescein-labeled HA demonstrated preferential adherence of the polysaccharide to interstitial, vascular, and pleural elastic fibers (Fig 2 ).^{6 7}

View larger version (119K): [in this window] [in a new window] [Download PPT slide]   Figure 1. Photomicrographs of HA-treated lungs (top) and untreated lungs (bottom), 1 week following intratracheal instillation of human neutrophil elastase (hematoxylin-eosin, original x100). Significantly less airspace enlargement is noted in lungs receiving HA.

View larger version (122K): [in this window] [in a new window] [Download PPT slide]   Figure 2. Aerosolized fluorescein-labeled HA preferentially binds to pulmonary elastic fibers (original x800).

	Proposed Role of Nebulized HA in Improving Pulmonary Mechanics

TOP Abstract Introduction Experimental Findings Proposed Role of Nebulized... The Potential Effect of... Conclusions References

 
In addition to physically protecting elastic fibers from disruption, it is hypothesized that exogenously administered HA may prevent airspace enlargement by virtue of its ability to retain water. In solution, negatively charged carboxyl groups attached to the saccharide moieties repel one another, expanding the domain of HA and allowing it to entrap water (Fig 3 ).¹⁷ The loss of HA from the lung interstitium has been shown to reduce extravascular water content, demonstrating the importance of this polysaccharide in regulating lung hydration.¹⁴

View larger version (34K): [in this window] [in a new window] [Download PPT slide]   Figure 3. HA undergoes expansion in solution, increasing its capacity to entrap water.

	The Potential Effect of HA-Induced Water Retention on Elastic Fiber Mechanics

TOP Abstract Introduction Experimental Findings Proposed Role of Nebulized... The Potential Effect of... Conclusions References

 
Elastic fibers are highly distensible and help to provide the force necessary to expel air from the lungs during expiration.²¹ Energy is stored within the fibers when they are distended by inhalation and is released as they recoil during exhalation.^{18 19 20} The fibers have a highly specialized structure, consisting of an amorphous core elastin protein surrounded by layers of microfibrils.²² The elastin protein is composed of networks of cross-linked peptide chains containing hydrophobic domains that contribute to the elastic properties of the fibers.²³

Aside from the absolute numbers of elastic fibers in the lung, changes in their structure may affect lung mechanics. Elastic fibers can become frayed and lose elasticity without an actual decrease in overall quantity. Indeed, large accumulations of elastic fibers in sun-exposed skin (ie, solar elastosis) are nevertheless associated with wrinkling.²⁴ This suggests that other factors are important in maintaining the elasticity of tissues.

One additional component that may play an important role in pulmonary mechanics is interstitial water content. In the case of elastic fibers, interactions between water molecules and hydrophobic amino acid groups within the core elastin protein are largely responsible for elastic recoil. The absorption of water onto nonpolar hydrophobic groups during the extension of elastin results in a large positive free energy change that contributes to the storage of elastic energy.²⁰ A decrease in the availability of water can compromise this process, reducing elastic fiber recoil. Furthermore, water facilitates the swelling of the elastin molecules, thereby increasing their random energy state and enhancing recoil as a result of the increased loss of entropy during distention.²⁰

Resistance to stretching of the elastic fibers also may be dependent on the intramolecular forces of attraction among the elastin peptide chains themselves. Removing water molecules decreases the distance between the elastin peptide chains, enhancing their cohesion and reducing the distensibility of the fibers.²⁵ At the extreme, the complete absence of water yields an elastic modulus approaching that of glass, thereby preventing any significant distention of elastic fibers.²⁶

In the well-hydrated lung, the forces facilitating the distention and recoil of elastic fibers will predominate, permitting the efficient movement of air and proper gas exchange. If the water concentration decreases, however, the mechanical properties of the elastic fibers may deteriorate. Marked decreases in hydration may cause the fibers to become brittle, making them vulnerable to rupture under strain. The resulting breakage of the fibers could mimic the effects of enzymatic degradation. Air would become trapped in the lung with resultant alveolar distention and rupture.

This type of dehydration injury to elastic fibers is likely to occur in pulmonary emphysema. The loss of water may be due to decreased blood flow to the lung as a result of damage to pulmonary vessels, but may also be caused by injury to the extracellular matrix. Studies²⁷ of human lungs with emphysema have demonstrated a proportional decrease in HA compared to other glycosaminoglycans, which would adversely affect extravascular water content.

It is anticipated that the administration of HA to emphysema patients will increase the density of water around dehydrated elastic fibers. This process might be enhanced by the self-aggregation of HA,¹² which could further entrap water in the proximity of elastic fibers. Such hydration should improve the recoil properties of the elastic fibers by facilitating the availability of water to hydrophobic groups within the elastin polypeptide chains. The elastin chains also would become more disordered in response to hydration, permitting greater storage of elastic energy during distention, when entropy is lost.

Since much of the water retained by HA would be trapped within its molecular domain and would not be freely available to the lung, it should not produce symptoms of pulmonary edema. Unlike congestive heart failure or ARDS, in which the accumulation of alveolar lung water can adversely affect respiration, the hydrating effect of exogenously administered HA would be self-limited and localized to the extracellular matrix.

While it remains to be seen what effect HA will actually have on pulmonary mechanics, there currently exists some indirect evidence that it may increase lung water content. Rats exposed to nebulized HA for 14 days showed a dose-dependent increase in lung weight that was not due to cellular proliferation (unpublished data). Microscopically, these animals showed no evidence of pulmonary edema, suggesting that any increase in lung water was bound up in the extracellular matrix.

	Conclusions

TOP Abstract Introduction Experimental Findings Proposed Role of Nebulized... The Potential Effect of... Conclusions References

 
The use of nebulized HA as a potential treatment for pulmonary emphysema represents a different approach to treating disease, one that is directed toward the extracellular matrix rather than intracellular processes. The proposed mechanisms of action of HA discussed in this article may have broad applicability to a number of conditions involving injury to extracellular matrix components, such as osteoarthritis (which is already being treated with exogenous HA), vascular aneurysms, and skin aging.^{28 29 30}

In designing a therapeutic regimen for patients with pulmonary emphysema, an important factor to consider will be potential toxicity resulting from prolonged exposure to HA. Possible accumulation of this agent in the lung might induce inflammatory changes. While 14-day exposures of both rats and dogs to suitable concentrations of HA did not reveal any significant adverse pulmonary effects (unpublished data), additional studies are necessary to rule out complications arising from prolonged treatment. Clinical trials will require careful patient monitoring to detect possible signs of diminished lung function.

With regard to the potential therapeutic efficacy of HA, the long-term protection of elastic fibers from injury may ultimately prove to be more important than any initial enhancement of lung mechanics due to increased hydration. Since pulmonary emphysema generally results in a gradual loss of lung function, even a small decrease in its rate of progression could significantly delay the worst effects of the disease to extreme old age, effectively eliminating them from the lives of most patients.

	Footnotes

 
Abbreviation: HA = hyaluronan

This work was supported by the Ned Doyle Foundation, the Charles A. Mastronardi Fund, the Franklyn Bracken Fund, and the James P. Mara Center for Lung Disease at the St. Luke’s-Roosevelt Hospital Center.

The authors are cofounders of Exhale Therapeutics, which is commercializing the use of aerosolized hyaluronan to treat pulmonary emphysema.

Received for publication December 17, 2002. Accepted for publication June 12, 2003.

	References

TOP Abstract Introduction Experimental Findings Proposed Role of Nebulized... The Potential Effect of... Conclusions References

 

1. Gross, P, Babyak, MA, Tolker, E, et al (1964) Enzymatically produced pulmonary emphysema: a preliminary report. J Occup Med 6,481-484[Medline]
2. Laurell, C-B, Eriksson, S The electrophoretic ₁-globulin pattern of serum in ₁-antitrypsin deficiency. Scand J Clin Lab Invest 1963;15,132-140[ISI]
3. Janoff, A Elastases and emphysema: current assessment of the protease-antiprotease hypothesis. Am Rev Respir Dis 1985;132,417-433[ISI][Medline]
4. Senior, RM, Kuhn, C, 3rd The pathogenesis of emphysema. Fishman, AP eds. Pulmonary diseases and disorders 2nd ed. 1988,1209-1218 McGraw-Hill. New York, NY:
5. Cantor, JO, Cerreta, JM, Keller, S, et al Modulation of airspace enlargement in elastase-induced emphysema by intratracheal instillment of hyaluronidase and hyaluronic acid. Exp Lung Res 1995;21,423-436[ISI][Medline]
6. Cantor, JO, Cerreta, JM, Armand, G, et al Further investigation of the use of intratracheally administered hyaluronic acid to ameliorate elastase-induced emphysema. Exp Lung Res 1997;23,229-244[ISI][Medline]
7. Cantor, JO, Cerreta, JM, Armand, G, et al Aerosolized hyaluronic acid decreases alveolar injury induced by human neutrophil elastase. Proc Soc Exp Biol Med 1998;217,471-475[Abstract]
8. Cantor, JO, Shteyngart, B, Cerreta, JM, et al The effect of hyaluronan on elastic fiber injury in vitro and elastase-induced airspace enlargement in vivo. Proc Soc Exp Biol Med 2000;225,65-71[Abstract/Free Full Text]
9. Barnes, PJ Novel approaches and target for treatment of chronic obstructive pulmonary disease. Am J Respir Crit Care Med 1999;160,S72-S79[Abstract/Free Full Text]
10. Calverley, PM Modern treatment of chronic obstructive pulmonary disease. Eur Respir J 2001;34,60s-66s
11. Chitkara, RK, Sarinas, PS Recent advances in diagnosis and management of chronic bronchitis and emphysema. Curr Opin Pulm Med 2002;8,126-136[CrossRef][ISI][Medline]
12. Scott, JE, Cummings, C, Brass, A, et al Secondary and tertiary structures of hyaluronan in aqueous solution, investigated by rotary shadowing-electron microscopy and computer simulation: hyaluronan is a very efficient network-forming polymer. Biochem J 1991;274,699-705
13. Johnsson, H, Eriksson, L, Jonzon, A, et al Lung hyaluronan and water content in preterm and term rabbit pups exposed to oxygen and air. Pediatr Res 1998;44,716-722[ISI][Medline]
14. Bhattacharya, J, Cruz, T, Bhattacharya, S, et al Hyaluronan affects extravascular water in lungs of unanesthetized rabbits. J Appl Physiol 1989;66,2595-2599[Abstract/Free Full Text]
15. Cantor, JO, Cerreta, JM, Armand, G, et al Pulmonary air-space enlargement induced by intratracheal instillment of hyaluronidase and concomitant exposure to 60% oxygen. Exp Lung Res 1993;19,177-192[ISI][Medline]
16. Shapiro, SD, Kobayashi, DK, Ley, TJ Cloning and characterization of a unique elastolytic metalloproteinase produced by human alveolar macrophages. J Biol Chem 1993;268,23824-23829[Abstract/Free Full Text]
17. Toole, BP Glycosaminoglycans and morphogenesis. Hay, ED eds. Cell biology of extracellular matrix 1981,259-294 Plenum. New York, NY:
18. Li, B, Alonso, DO, Bennion, BJ, et al Hydrophobic hydration is an important source of elasticity in elastin-based biopolymers. J Am Chem Soc 2001;123,11991-11998[CrossRef][ISI][Medline]
19. Wasserman, ZR, Salemme, FR A molecular dynamics investigation of the elastomeric restoring force in elastin. Biopolymers 1990;29,1613-1631[CrossRef][ISI][Medline]
20. Gosline, JM The role of hydrophobic interactions in the swelling of elastin. Sandberg, LB Gray, WR Franzblau, C eds. Advances in experimental medicine and biology (vol 79) 1977,621-631 Plenum. New York, NY:
21. Mariani, TJ, Sandefur, S, Pierce, RA Elastin in lung development. Exp Lung Res 1997;23,131-145[ISI][Medline]
22. Mecham, RP Elastin synthesis and fiber assembly. Ann N Y Acad Sci 1991;624,137-146[ISI][Medline]
23. Rosenbloom, J, Abrams, WR, Mecham, R Extracellular matrix 4: the elastic fiber. FASEB J 1993;7,1208-1218[Abstract]
24. Suwabe, H, Serizawa, A, Kajiwara, H, et al Degenerative processes of elastic fibers in sun-protected and sun-exposed skin: immunoelectron microscopic observation of elastin, fibrillin-1, amyloid P component, lysozyme, and ₁-antitrypsin. Pathol Int 1999;49,391-402[CrossRef][ISI][Medline]
25. Kendall, K Molecular adhesion and its applications. 2001,103-131 Plenum. New York, NY:
26. Hoeve, CAJ The elasticity in the presence of diluents. Sandberg, LB Gray, WR Franzblau, C eds. Advances in experimental medicine and biology 1977;vol 79,607-619 Plenum. New York, NY:
27. Konno, K, Arai, H, Motmiya, M, et al A biochemical study of glycosaminoglycans (mucopolysaccharides) in emphysematous and in aged lungs. Am Rev Respir Dis 1982;126,797-801[ISI][Medline]
28. Graf, J, Neusel, E, Schneider, E, et al Intra-articular treatment with hyaluronic acid in osteoarthritis of the knee joint: a controlled clinical trial versus mucopolysaccharide polysulfuric acid ester. Clin Exp Rheumatol 1993;11,367-372[ISI][Medline]
29. Gandhi, RH, Irizarry, E, Cantor, JO, et al Analysis of elastin cross-linking and the connective tissue matrix of abdominal aortic aneurysms. Surgery 1994;115,617-620[ISI][Medline]
30. Fisher, GJ, Wang, ZQ, Datta, SC, et al Pathophysiology of premature aging induced by ultraviolet light. N Engl J Med 1997;337,1419-1428[Abstract/Free Full Text]

This article has been cited by other articles:

				R. Buhl and S. G. Farmer Future Directions in the Pharmacologic Therapy of Chronic Obstructive Pulmonary Disease Proceedings of the ATS, April 1, 2005; 2(1): 83 - 93. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) Free Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Add to My Personal Article Archive Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (4) Citing Articles via Google Scholar Google Scholar Articles by Cantor, J. O. Articles by Turino, G. M. Search for Related Content PubMed PubMed Citation Articles by Cantor, J. O. Articles by Turino, G. M.