Experimental Emphysema

Microvascular architecture of the elastase emphysemic hamster lung

Vascular corrosion casts of normal and elastase-induced emphysemic hamster lungs, prepared with a low viscosity resin mixture consisting of Mercox and Sevriton, were observed by scanning electron microscopy. Casts were quantitated by measuring vascular volume or determining non-alveolar air space using confocal laser scanning microscopy. Normal lung casts were characterized by well-organized fields of alveoli (about 70 microns in diameter) connected by distinct alveolar ducts. Emphysemic lung casts exhibited numerous bullae (often as large as 0.5 mm in diameter). The vasculature of the bullae indicated that they were formed by destruction of alveolar walls and subsequent coalescence of numerous alveolae. Remnants of alveolar walls, consisting of shallow ridges of capillaries, lined the bases of the bullae. Vascular volumes expressed as cast volume/total tissue volume were calculated at 20% and 12% for uninflated and inflated lungs, respectively, for both control and emphysemic lungs. Four months after elastase instillation, nonalveolar air space of the emphysemic lungs was increased by 73% over controls. These observations indicate that elastase emphysema results, initially, in remodeling of the alveolar structure (bullae formation) and loss of surface area for gas exchange, rather than from extensive loss of vasculature. Vascular corrosion casting is a useful technique for monitoring emphysema both morphologically and quantitatively.

Elastase and papain inhibition by serum of mammals

The protease-antiprotease imbalance concept has gained wide acceptance in reference to experimental animal models of human pulmonary emphysema. The destructive process may be induced by proteolytic enzymes such as porcine pancreas elastase (E) or papain (P), or by oxidants such as chloramine T (CT) which cause inactivation of alpha-1-antiprotease. The susceptibility to development of severe emphysema has been found to differ among animal species. We investigated the inhibition of elastase and papain by serum of seven species (rat, dog, human, rabbit, sheep, hamster, mini pig) and the effect of CT on serum inhibition. The relative inhibitor concentration of serum was expressed in terms of its inhibitor capacity for elastase and papain (EIC and PIC) defined as number of inhibited units (U) of enzyme catalysed hydrolysis of chromogenic peptide substrate (SAPNA and BAPNA) per unit of serum. The effect of CT on enzyme inhibition was quantified in terms of fractional loss of inhibition relative to control. The serum concentration of inhibitor was highest in the rat (EIC 8642 +/- 989 microU/microliter, PIC 214.2 +/- 110.3 microU/microliter; means +/- SD). Next in order of decreasing EICs were dog, human, rabbit, sheep, hamster, and mini pig exhibiting the lowest EIC (2523 +/- 184 microU/microliter) while sheep had lowest PIC (39.6 +/- 3.5 microU/microliter). The EIC/PIC ratio varied from 20 (mini pig) to about 100. The reduction of elastase inhibition after CT exposure of serum was high (80-100%) in rat, dog, human, and hamster, moderate (40%) in mini pig and rabbit, and low (10%) in sheep. Because papain was directly affected by CT the effect of CT on papain inhibition could not be analysed. The data suggest that the intrinsic antiprotease and antioxidant screen varies among experimental animals. For the purpose of animal models of emphysema, hamster appears to be most susceptible to the progressive destruction of lung parenchyma elicited by experimental burden of proteases or oxidants.