Characterization and regulation of a CHO cell line stably expressing human serotonin N-acetyltransferase (EC 2.3.1.87)

Current melatonin research is essentially based on the finding of new molecular tools, including synthetic or natural agonists and antagonists for the melatonin receptors and synthetic inhibitors of the enzymes involved in its biosynthesis. Indeed, the use of these compounds will improve our understanding of some of the numerous mechanisms of action of melatonin. The present report deals with the establishment and description of a new cell line expressing in a stable manner human arylalkylamine-N-acetyltransferase (AANAT, E.C.2.3.1.87). This new cellular system permits one to check the capacity of newly discovered inhibitors to penetrate the cell and reach their target. Some emphasis is put on inhibitors of the bromoacetyltryptamine family since these precursor compounds form in situ bisubstrate inhibitors with strong affinity for the human enzyme. AANAT is known to undergo complex and rapid regulation by a subtle balance between extremely fast catabolism and protection against it, both due to serine phosphorylation. In the present report, this phosphorylation is shown to occur in vitro after incubation with several kinases (rho-kinase, chk-1, protein kinase A) but not with protein kinase C. Phosphorylation enhances the specific activity of the enzyme by a factor of two to five. This phosphorylation is also shown to occur after treatment of the cell with compounds such as forskolin and rolipram that enhance or protect the intracellular pool of cAMP or the cell-permeable cAMP analogue, dioctanoyl-cAMP. The specificity of the cellular model was assessed using a series of substrates and inhibitors of AANAT already described in the literature, and the characteristics of this cellular system are shown to correspond with those reported for the purified enzyme. This cell line was used to screen libraries of compounds in a living system and led to the discovery of several potent specific and non-toxic AANAT inhibitors.

[The Ottawa ankle guidelines: analysis of their validity as clinical decision guidelines in the indication of X-rays for ankle and/or middle-foot injuries]

OBJECTIVE

To analyse the validity of the Ottawa ankle guidelines (OAG) as clinical decision guidelines in the indications of X-rays for ankle and/or middle-foot traumas in primary care.

DESIGN

Observational, with application of the OAG and prospective measurement of the results.Setting. Hospital casualty.

PATIENTS

Adults who attended casualty for ankle or middle-foot traumas between 1st June 1999 and 31th March 2000. Criteria for exclusion were: under 18, pregnancy, grave sensory and/or awareness disturbances, multi-trauma or multi-contusion patients, traumas over a week old, skin lesions as side-effects of the trauma, X-ray in other department, high inflammation or oedema hindering palpation of bone protuberances.

MEASUREMENTS

Application of the OAG and X-ray on all patients, regardless of the result of the OAG. Calculation of sensitivity, negative predictive value, specificity and positive predictive value.

RESULTS

56 of a sample of 494 patients had a fracture (11.34%), 34 in the malleolus area (6.9%) and 22 in the middle-foot area (4.44%). OAG sensitivity was 96.43% (95% CI, 94.8-98). Negative predictive value was 97.22% (95.77-98.67). Specificity was 15.98% (12.75-19.21), and positive predictive value was 12.8% (9.86-15.74).

CONCLUSIONS

The OAG are valid in primary care as guidelines to decide whether to request X-rays for patients with ankle or middle-foot traumas.