Throughout this application, various publications are referenced by numbers. The full citations are listed at the end of the specification immediately preceding the claims.
Elastic fibers are a prominent component of the extracellular matrix and play an important role in determining the mechanical properties of tissues. By virtue of their distensibility, elastic fibers permit tissues to function normally despite the application of external forces. In the lung, for example, interstitial and pleural elastic fibers facilitate tissue recoil following inspiration, preventing permanent distention of the organ and maintaining the flow of gases within airways. Damage to these fibers causes dilatation and rupture of alveoli, resulting in pulmonary emphysema (1,2).
Despite the importance of maintaining the integrity of elastic fibers, there is currently no effective means of protecting them from damage. Since these fibers are susceptible to degradation by enzymes known as elastases, various elastase inhibitors have been tested as a possible means of preventing elastic fiber injury (1,3). In particular, a naturally occurring inhibitor, alpha-1-antiproteinase, has recently been given to individuals who normally lack this inhibitor in an attempt to slow the progression of elastic fiber breakdown which leads to pulmonary emphysema (4). Such a treatment strategy assumes, however, that elastic fiber injury is caused by a specific type of biochemical derangement, i.e. alpha-1-antiproteinase deficiency. If damage to these fibers represents a more general reaction to a variety of insults (with elastases playing a variable role), then enzyme inhibition may have only limited efficacy.
To determine if mechanisms other than elastase injury are involved in elastic fiber breakdown, a series of experiments were performed by this laboratory involving both the induction and modification of experimental emphysema with agents other than elastases. Experiments using hyaluronidase and 60 percent oxygen showed that significant damage to elastic fibers occurs only when both agents are given concomitantly, suggesting the possibility that hyaluronidase may facilitate the breakdown of elastic fibers by making them more accessible to injury (5). This hypothesis was further tested by giving hamsters intratracheal instillments of hyaluronidase, followed by elastase, and then examining the lungs for air-space enlargement (6). The findings indicated that pretreatment with hyaluronidase enhances elastase-induced emphysema. Furthermore, it was found that intratracheally administered hyaluronic acid (HA) had the opposite effect, significantly reducing elastase-induced air-space enlargement. This latter finding resulted in a U.S. patent on the use of intratracheally administered HA to ameliorate emphysema (5,663,003). The current application describes the underlying mechanism responsible for the protective effect of HA, which was previously unknown, and the methods described below are specifically directed to the prevention of injury to tissue elastic fibers.
As will be shown, the protective effect of HA does not involve inhibition of elastase, but instead depends upon direct interaction with elastic fibers. Both in vivo and in vitro studies using fluorescein-labeled HA, indicate that this polysaccharide preferentially binds to and coats elastic fibers, protecting them from injury. Such binding may be related to the numerous carboxyl and hydroxyl groups within HA which are possibly attracted to elastic fibers by one or more of the following mechanisms: 1) hydrogen bonds, 2) electrostatic bonds, or 3) van der Waals forces. Since many polysaccharides or other carbohydrate moieties share similar chemical properties, it may be possible to use them in a like manner to coat elastic fibers.
The subject invention is directed to the prevention of injury to mammalian tissue elastic fibers by administration of HA or any other polysaccharide or carbohydrate moiety that binds to and coats elastic fibers, thereby protecting these fibers from enzymes, oxidants, or other injurious agents. Studies by the inventor (JOC) have shown that HA preferentially binds to elastic fibers in the lung and prevents destruction of alveoli by intratracheally administered elastases. Corresponding in vitro experiments demonstrate that binding of HA to elastic fibers interferes with the ability of elastase to damage the fibers. Since other polysaccharides share similar chemical properties with HA, it may be possible to use them in a like manner to coat elastic fibers. Consequently, the invention comprises all forms of naturally occurring, chemically modified, or artificially synthesized compounds which are wholly or partially composed of polysaccharides or other carbohydrate moieties and which are capable of covalently or noncovalently binding to elastic fibers. Such compounds could be administered orally, subcutaneously, intravenously, intratracheally, or by any other route deemed efficacious. They may be administered alone or with a carrier such as saline solution, DMSO, alcohol, or water. The effective daily amount of the compound(s) is from about 0.1 xcexcg/kg to about 1 mg/kg body weight.