T.W. Mittag

Role of oxygen radicals in ocular inflammation and cellular damage.

Oxyradicals probably play a major role in a number of specific pathological conditions of intraocular tissues, such as cataract formation and retinal degeneration. This paper reviews some of the mechanistic concepts relating to tissue damage by highly reactive oxidants derived from endogenous precursors, hydrogen peroxide and superoxide. Experimental generation of superoxide in the anterior chamber of the rabbit eye showed leucocyte infiltration to be the principal acute response occurring in 4 hr. This finding suggests that superoxide may play a significant role in the ocular inflammatory response, possibly by reacting with a precursor substance in the aqueous humor to produce a chemotactic factor as has been previously found for blood plasma.

Desensitization of the β-adrenergic receptor-adenylate cyclase complex in rabbit iris-ciliary body induced by topical epinephrine

Topical treatment of the rabbit eye with three successive doses of 2% epinephrine bitartrate alters the in vitro drug response of the β-adrenergic receptor-adenylate cyclase enzyme complex in membrane fragments prepared from the iris and ciliary body. Treated tissues showed a significant decrease in activation of adenylate cyclase by guanosine triphosphate (100 μ m ), guanosine 5′-diphospho-imido phosphate (0·2 μ m ), and by isoproterenol (10 μ m ) in presence of either of the above guanyl nucleotides but showed no significant change in basal adenylate cyclase activity or in activity stimulated by fluoride (10 m m ). The epinephrine-induced desensitization of β-adrenergic receptor-coupled adenylate cyclase is associated with a functional impairment of the guanyl nucleotide regulatory protein and possibly with a small decrease in the number of affinity of β -adrenergic receptor ligand binding sites. Agonist-induced changes in receptors and in their molecular effector systems represent basic mechanisms for alteration of tissue responses to drugs and may thus be involved in the therapy of glaucoma with chronic topical epinephrine.

Analysis of false negative results in the immunoassay for anti-acetylcholine receptor antibodies in myasthenia gravis

Possible causes for the failure of immunoassays to detect anti-acetylcholine receptor activity in serum from confirmed myasthenia gravis (MG) patients were investigated. A more sensitive assay, using Protein A to trap immune complexes (ARIA), was applied to 65 MG sera which were negative in the usual assay and to 42 normal human sera. Normal and negative MG sera had antibody (Ab) activity in the same range (50-70 pM). Titers present in 70% of normal sera appeared to be specific antireceptor antibodies as defined by tests for antigen specificity. Thus, higher sensitivity assays did not improve discrimination of MG from normals. In a second group of 108 MG sera studied, 48 were negative by the usual assay criteria in a rat acetylcholine receptor immunoassay. Further detailed analysis of this negative group showed that 3/48 had IgG3 antibody not detectable in the test, 14/48 had Abs recognizing human receptor determinants exclusively, 29/48 had toxin blocking Abs not determined by immunoassays, and 6/48 were negative in all tests. The results indicate that the exclusive occurrence of toxin-blocking antibodies in MG subjects is a major factor contributing to false negatives in the ARIA test. Estimates of the amount of Abs with this functionality indicated that they are present in very much smaller amounts than other classes of anti-receptor Abs. Degree of blocking activity in patient serum showed a fair correlation with severity of disease. Thus, blocking antibodies appear capable of causing all degrees of disease severity in the absence of other types of antireceptor Abs. The development of a sensitive and quantitative in vitro assay for blocking antibodies combined with the usual immunoassay would be a major improvement for a MG diagnostic test, with greater than 94% positivity predicted.