Subacute tissue reaction

Bioerodable materials in current use are limited to applications that do not require long-term strength retention. It is acknowledged by the medical profession that problems exist with the current practices of bone fracture fixation. Two serious problems are osteoporosis due to stress shielding [1-3] and necessary second operations for device removal after bone healing. To alleviate these problems, polymers of a-hydroxy acids such as lactic and glycolic acid are being explored. They have shown potential utility as biocompatible, fully resorbable implant devices. The biocompatibility of poly(a-hydroxy acids) has been known for some time from in vivo acute and subacute tissue reaction [4], as well as in vitro cytotoxicity response [5]. Sutures of these materials have been in use now for many years. 

In subacute MI, characterized histologically by the proliferation of granulation tissue and fibrous tissue, positive reaction for cleaved caspase-3 was observed in mononuclear inflammatory cells, myofibroblasts, and vascular endothelial cells (Fig. 5B). The number of positive cells decreased as granulation tissue was transforming into a fibrous scar [123]. 

Fig. 5. Proliferation of granulation tissue in subacute MI. (A) Hematoxylin and eosin. (B) Immunohistochemical staining for activated caspase-3 positive reaction in granulation tissue, mononuclear inflammatory cells, myofibroblasts (M), and vascular endothelial cells (E).

Taskinen E, Tukiainen P, Sovijarvi AR. Nitrofurantoin-induced alterations in pulmonary tissue. A report on five patients with acute or subacute reactions. Acta Pathol Microbiol Scand [A] 1977 85(5) 713-20. 

Photosensitivity. Skin reddening due to an abnormal reaction to sunlight. A characteristic symptom of systemic autoimmune diseases (e.g. systemic lupus erythematosus, mixed connective tissue disease), cutaneous and subacute cutaneous lupus erythematosus. 

The rates of aU the reactions in the figure are important, too. If the rate of the toxic mechanism in the blood and the rates at which the toxicant affects other organ systems are faster than the rate at which the toxicant moves from the blood to the fiver, then the toxic effect may be exerted before the fiver can perform its heroic function. The same could be said of the B-F equilibrium. If the B-F equilibrium is fast enough and the toxicant can be stored in the fatty tissue (where even at high levels it cannot exert its toxic effect while safely stored in the fatty tissue), then even though there may be an acutely toxic level in the body overall, since most of the toxicant is stored in fat, the level in the blood would be at a subacute level. 

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