Publications

We demonstrated earlier that the heme in cytochrome P450 enzymes of the CYP4A family is covalently attached to the protein through an I-helix glutamic acid residue [Hoch, U., and Ortiz de Montellano, P. R. (2001) J. Biol. Chem. 276, 11339-11346]. As the critical glutamic acid residue is conserved in many members of the CYP4F class of cytochrome P450 enzymes, we investigated covalent heme binding in this family of enzymes. Chromatographic analysis indicates that the heme is covalently bound in CYP4F1 and CYP4F4, which have the required glutamic acid residue, but not in CYP4F5 and CYP4F6, which do not. Catalytic turnover of CYP4F4 with NADPH-cytochrome P450 reductase shows that the heme is covalently bound through an autocatalytic process. Analysis of the prosthetic group in the CYP4F5 G330E mutant, into which the glutamic acid has been reintroduced, shows that the heme is partially covalently bound and partially converted to noncovalently bound 5-hydroxymethylheme. The modified heme presumably arises by trapping of a 5-methyl carbocation intermediate by a water molecule. CYP4F proteins thus autocatalytically bind their heme groups covalently in a process that requires a glutamic acid both to generate a reactive (cationic) form of the heme methyl and to trap it to give the ester bond.

BACKGROUND

There are few effective treatments for ankylosing spondylitis, which causes substantial morbidity. Because of the central role of tumor necrosis factor alpha in the spondyloarthritides, we performed a randomized, double-blind, placebo-controlled trial of etanercept, a recombinant human tumor necrosis factor receptor (p75):Fc fusion protein, in patients with ankylosing spondylitis.

METHODS

Forty patients with active, inflammatory ankylosing spondylitis were randomly assigned to receive twice-weekly subcutaneous injections of etanercept (25 mg) or placebo for four months. The primary end point was a composite of improvements in measures of morning stiffness, spinal pain, functioning, the patient's global assessment of disease activity, and joint swelling. Patients were allowed to continue taking nonsteroidal antiinflammatory drugs, oral corticosteriods (< or =10 mg per day), and disease-modifying antirheumatic drugs at stable doses during the trial.

RESULTS

Treatment with etanercept resulted in significant and sustained improvement. At four months, 80 percent of the patients in the etanercept group had a treatment response, as compared with 30 percent of those in the placebo group (P=0.004). Improvements over base-line values for various measures of disease activity, including morning stiffness, spinal pain, functioning, quality of life, enthesitis, chest expansion, erythrocyte sedimentation rate, and C-reactive protein, were significantly greater in the etanercept group. Longitudinal analysis showed that the treatment response was rapid and did not diminish over time. Etanercept was well tolerated, with no significant differences in rates of adverse events between the two groups.

CONCLUSIONS

Treatment with etanercept for four months resulted in rapid, significant, and sustained improvement in patients with ankylosing spondylitis.