Anesthesiology: regional anesthesia in children

The Scientific Board of the California Medical Association presents the following inventory of items of progress in anesthesiology. Each item, in the judgement of a panel of knowledge physicians, has recently become reasonably firmly established, both as to scientific fact and important clinical significance. The items are presented in simple epitome and an authoritative reference, both to the item itself and to the subject as a whole, is generally given for those who may be unfamiliar with a particular item. The purpose is to assist busy practitioners, students, research workers, or scholars to stay abreast of these items of progress in anesthesiology that have recently achieved a substantial degree of authoritative acceptance, whether in their own field of special interest or another.The items of progress listed below were selected by the Advisory Panel to the Section on Anesthesiology of the California Medical Association and the summaries were prepared under its direction.     

Interleukin 1 production by the human monocyte cell line U937 requires a lymphokine induction signal distinct from interleukin 2 or interferons

A soluble product from cloned human T lymphocytes is capable of stimulating U937 cells, a line of human monocytes, to produce interleukin 1 (IL 1). We previously reported that U937 cells exposed to T lymphocyte-conditioned medium secrete mononuclear cell factor (MCF), which increases collagenase and prostaglandin E2 production by adherent rheumatoid synovial cells. Whereas structural and functional homologies between lymphocyte-activating factor (LAF, or IL 1) and MCF were described, previous attempts to measure LAF secretion by lymphokine-stimulated U937 cells were unsuccessful. Although the crude supernatants of cultured U937 cells exposed to medium from lectin-stimulated peripheral blood or cloned T lymphocytes contained MCF activity, no LAF activity was detected. After these crude supernatants were chromatographed on Ultrogel AcA54, however, and the fractions were individually assayed for IL 1, MCF and LAF activities were coeluted with apparent m.w. approximately 14,000 to 23,000. The inability to detect LAF activity in the unfractionated medium was accounted for by an inhibitor of lymphocyte proliferation present in fractions of higher m.w. The T lymphocyte product that stimulated U937 cell maturation and monokine production was secreted in response to lectin-stimulation in a dose-dependent fashion. Although we have previously demonstrated that the hormone 1,25-dihydroxyvitamin D3 caused maturational changes in U937 cells, and other investigators have reported effects of alpha and gamma interferon, these changes are dissociable from IL 1 production. Thus, a distinct lymphocyte-derived signal, necessary for the production of IL 1 by U937 cells, can be identified and dissociated from other biologic products that cause "maturational" changes. The detection of LAF activity in U937 cell supernatants requires the removal of an inhibitor of lymphocyte proliferation.     

The Activity of Collagenase-1 Is Required for Keratinocyte Migration on a Type I Collagen Matrix

We have shown in a variety of human wounds that collagenase-1 (MMP-1), a matrix metalloproteinase that cleaves fibrillar type I collagen, is invariably expressed by basal keratinocytes migrating across the dermal matrix. Furthermore, we have demonstrated that MMP-1 expression is induced in primary keratinocytes by contact with native type I collagen and not by basement membrane proteins or by other components of the dermal or provisional (wound) matrix. Based on these observations, we hypothesized that the catalytic activity of MMP-1 is necessary for keratinocyte migration on type I collagen. To test this idea, we assessed keratinocyte motility on type I collagen using colony dispersion and colloidal gold migration assays. In both assays, primary human keratinocytes migrated efficiently on collagen. The specificity of MMP-1 in promoting cell movement was demonstrated in four distinct experiments. One, keratinocyte migration was completely blocked by peptide hydroxymates, which are potent inhibitors of the catalytic activity of MMPs. Two, HaCaTs, a line of human keratinocytes that do not express MMP-1 in response to collagen, did not migrate on a type I collagen matrix but moved efficiently on denatured type I collagen (gelatin). EGF, which induces MMP-I production by HaCaT cells, resulted in the ability of these cells to migrate across a type I collagen matrix. Three, keratinocytes did not migrate on mutant type I collagen lacking the collagenase cleavage site, even though this substrate induced MMP-1 expression. Four, cell migration on collagen was completely blocked by recombinant tissue inhibitor of metalloproteinase-1 (TIMP-1) and by affinity-purified anti–MMP-1 antiserum. In addition, the collagen-mediated induction of collagenase-1 and migration of primary keratinocytes on collagen was blocked by antibodies against the α2 integrin subunit but not by antibodies against the α1 or α3 subunits. We propose that interaction of the α2β1 integrin with dermal collagen mediates induction of collagenase-1 in keratinocytes at the onset of healing and that the activity of collagenase-1 is needed to initiate cell movement. Furthermore, we propose that cleavage of dermal collagen provides keratinocytes with a mechanism to maintain their directionality during reepithelialization.     

Collagen synthesis by cultured skin fibroblasts from siblings with hydroxylysine-deficient collagen.

It has been previously shown that dermis from subjects with hydroxylysine-deficient collagen contains approximately 5% of normal levels of hydroxylysine and sonicates of skin fibroblasts contain less than 15% of normal levels of collagen lysyl hydroxylase activity. However, cultures of dermal fibroblasts from two siblings with hydroxylysine-deficient collagen (Ehlers-Danlos Syndrome Type VI) compared to fibroblasts from normal subjects synthesize collagen containing approximately 50% of normal amounts of hydroxylysine. The lysyl hydroxylase deficient cultures synthesize both Type I and Type III collagen in the same proportion as control cultures. Both alpha 1(I) and alpha 2 chains are similarly reduced in hydroxylysine content. Collagen prolyl hydroxylation by normal collagen lysyl hydroxylation is the same with or without ascorbate supplementation. In mutant cells the rate of prolyl hydroxylation measured after release of inhibition by alpha, alpha'-dipyridyl is the same as in control cells. The rate of lysyl hydroxylation is reduced in mutant cells but only to approximately 50% of normal.     

Proteolytic activity in human skin fibroblasts harvested with trypsin and its effect on measurements of collagen hydroxylase activities.

Lysates of human skin fibroblasts harvested without the use of trypsin do not contain detectable proteolytic activity, but when trypsin is used, lysates may contain activity equal to 10 ng of trypsin/10⁷ cells. The amount of cell lysate ordinarily examined for collagen prolyl and lysyl hydroxylase activity is sufficiently small that such amounts of trypsin have no observable effect on the unhydroxylated collagen substrate. Larger amounts of trypsin cause proteolysis of the unhydroxylated collagen substrate and a reduction of both prolyl and lysyl hydroxylation with lysyl hydroxylation more affected at low trypsin concentration than prolyl hydroxylation.