Metabolic inversion of (R)-ibuprofen. Formation of ibuprofenyl-coenzyme A

Ibuprofen [(racemic)2-(4-isobutylphenyl)propionic acid] undergoes metabolic inversion via formation, epimerization, and hydrolysis of the coenzyme A (CoA) thioester, ibuprofenyl-CoA. In this study, (R)-ibuprofen was incubated with either rat whole liver homogenate, human whole liver homogenate, rat liver mitochondria, or rat liver microsomes, and the formation of ibuprofenyl-CoA measured. Rat whole liver homogenate (Vmax/KM = 0.022 +/- 0.005 ml/min/mg protein) was approximately 4-fold more efficient at forming ibuprofenyl-CoA than human whole liver homogenate (Vmax/KM, = 0.005 +/- 0.004 ml/min/mg protein). Rat liver microsomes (Vmax/KM = 0.047 +/- 0.019 ml/min/mg protein) were approximately 2-fold more efficient than rat whole liver homogenate at forming ibuprofenyl-CoA, whereas rat liver mitochondria (Vmax/KM = 0.027 +/- 0.017 ml/min/mg protein) did not differ from whole liver homogenate. Palmitic (Ki = 0.005 mM) and octanoic acids (Ki = 0.19 mM) were capable of inhibiting ibuprofenyl-CoA formation, whereas propionic acid had no effect, suggesting the possible involvement of both long- and medium-chain fatty acyl-CoA synthetases. Of the xenobiotics tested, only bezafibrate (Ki = 0.85 mM) and (S)-ibuprofen (Ki = 0.095 mM in rats, 0.32 mM in human tissue) were capable of substantially inhibiting ibuprofenyl-CoA formation. Thus, it appears that the metabolic inversion of ibuprofen involves lipid-metabolizing pathways and may be affected by fatty acids or xenobiotics.

Ability of nifedipine to prolong parturition in rats

Rats were randomly assigned to treatments: (i) no surgery control; (ii) saline control; (iii) 0.25, 0.5, 1.0 or 2.0 micrograms nifedipine kg-1 min-1; or (iv) 5.0 micrograms ritodrine kg-1 min-1. All drug treatments increased the interval between pup deliveries compared with the no surgery and saline controls. Apparent complete tocolysis was observed in 20, 60, 80 and 80% of the animals receiving 0.5, 1.0 or 2.0 micrograms nifedipine kg-1 min-1 or 5.0 micrograms ritodrine kg-1 min-1, respectively. A positive pharmacodynamic relationship was observed for the nifedipine doses. Analysis of pup viability showed no statistically significant difference among treatments. Treatment with 2.0 micrograms nifedipine kg-1 min-1 gave a delay in pup delivery comparable to that with ritodrine.

Metabolic inversion of (R)-ibuprofen. Epimerization and hydrolysis of ibuprofenyl-coenzyme A

Ibuprofen [(racemic)2-(4-isobutylphenyl)propionic acid] has been proposed but not directly demonstrated to undergo unidirectional inversion from the (R)- to the (S)-configuration via a coenzyme A (CoA) thioester intermediate. Chemically synthesized (R)- and (S)-ibuprofenyl-CoA, and rat and human liver homogenates were used to investigate the relative rates of ibuprofenyl-CoA epimerization and hydrolysis. Rat whole liver homogenate completely epimerized (R)- or (S)-ibuprofenyl-CoA, whereas hydrolysis of this intermediate occurred at a much slower rate. Rat liver mitochondria was the most efficient at both epimerizing and hydrolyzing ibuprofenyl-CoA, whereas rat liver microsomes hydrolyzed ibuprofenyl-CoA at a rate similar to whole liver homogenate but had very little epimerization activity. Rat liver cytosol was the poorest at hydrolyzing ibuprofenyl-CoA but had substantial epimerization capability. Whole liver homogenate from human tissue was less efficient at epimerizing but as efficient at hydrolyzing ibuprofenyl-CoA as rat whole liver homogenate. No stereoselectivity of either epimerization or hydrolysis was noted for any of the enzyme preparations studied. This study demonstrates that the inversion of (R)-ibuprofen occurs, at least in part, via the epimerization of the metabolic intermediate, ibuprofenyl-CoA, in both rat and human liver tissues.

The effects of a salicylate, ibuprofen, and naproxen on the disposition of methotrexate in patients with rheumatoid arthritis

We have studied the pharmacokinetics of methotrexate in patients with rheumatoid arthritis concurrently treated with choline magnesium trisalicylate, ibuprofen, naproxen, or a non-NSAID analgesic (control treatment). The apparent systemic clearance of methotrexate was significantly reduced by all three treatments. Trisalicylate and ibuprofen both significantly reduced methotrexate renal clearance, but only the trisalicylate significantly displaced methotrexate from protein, increasing the fraction unbound by 28%. These data show that NSAIDs can affect the disposition of methotrexate, possibly increasing the potential for toxicity and necessitating dosage adjustments. However, large inter-subject variability precludes specific dosage recommendations.

Determination of the epimeric composition of ibuprofenyl-CoA

Ibuprofen [racemic2-(4-isobutylphenyl)propionic acid] is a 2-arylpropionic acid nonsteroidal anti-inflammatory drug which undergoes unidirectional, R to S chiral inversion in vivo. It has been proposed that this chiral inversion phenomenon occurs via a coenzyme A (CoA) thioester intermediate. To characterize the formation and metabolism of this metabolic intermediate, ibuprofenyl-CoA, reference standards were needed and thus the CoA derivatives of (R)-, (S)-, and racemic ibuprofen were chemically synthesized. An HPLC assay employing a C18 reverse-phase column was developed to quantitate "total" ibuprofenyl CoA. Samples collected from this assay were then analyzed for ibuprofenyl-CoA epimeric composition by chiral chromatography employing a Chiral-AGP alpha 1-acid glycoprotein column. The applicability of these methods was demonstrated by assessing (R)- and (S)-ibuprofenyl-CoA hydrolysis and epimerization following incubation with rat liver homogenates. Rat liver homogenate catalyzed the complete and rapid epimerization of ibuprofenyl-CoA and the rate constants for (R)- and (S)-ibuprofenyl-CoA hydrolysis were equal. ATP and CoA were found to inhibit rat liver-catalyzed ibuprofenyl-CoA hydrolysis by 70-80% with no effect on epimerization. Additionally, it was demonstrated that traditional indirect ibuprofenyl-CoA assays which employ basic hydrolysis result in erroneous epimeric ratio determinations due to chemical epimerization.

Calcium modulators: future agents, future uses

The calcium modulators have been a significant therapeutic advancement for the treatment of angina. Structural analogs of verapamil and nifedipine have been synthesized, as have structurally unique compounds. As the role of calcium in body processes is further elucidated, the efficacy of the calcium modulators is being evaluated for numerous disorders. It is anticipated that the newly synthesized compounds will have specificity toward particular body processes, thus providing efficacy with minimal side effects.