Therapeutic drug monitoring: antiarrhythmic drugs

Antiarrhythmic agents are traditionally classified according to Vaughan Williams into four classes of action. Class I antiarrhythmic agents include most of the drugs traditionally thought of as antiarrhythmics, and have as a common action, blockade of the fast-inward sodium channel on myocardium. These agents have a very significant toxicity, and while they are being used less, therapeutic drug monitoring (TDM) does significantly increase the safety with which they can be administered. Class II agents are antisympathetic drugs, particularly the b-adrenoceptor blockers. These are generally safe agents which do not normally require TDM. Class III antiarrhythmic agents include sotalol and amiodarone. TDM can be useful in the case of amiodarone to monitor compliance and toxicity but is generally of little value for sotalol. Class IV antiarrhythmic drugs are the calcium channel blockers verapamil and diltiazem. These are normally monitored by haemodynamic effects, rather than using TDM. Other agents which do not fall neatly into the Vaughan Williams classification include digoxin and perhexiline. TDM is very useful for monitoring the administration (and particularly the safety) of both of these agents.

The motility of demembranated human spermatozoa is inhibited by free calcium ion activities of 500 nmol/L or more

A number of studies have demonstrated that high calcium ion activities inhibit sperm motility, but little is known about the effect of different calcium activities close to the physiological range. Therefore, we investigated whether raising calcium activities within the submicromolar range would inhibit the motility of demembranated human spermatozoa. Spermatozoa were demembranated with Triton X-100 and motility was measured objectively by computer assisted semen analysis. Motility, reactivated by 1 mol adenosine 5'-triphosphate (AlphaTauP)/L, was short lived, with maximum activity only sustained for about 1 min. Reactivated motility was not affected by 50 micromol cAMP/L. The amplitude of lateral head displacement was significantly greater at room temperature than at 37 degrees C, but there were no significant differences between the percentage of sperm motile or their velocity at the two temperatures. The calcium buffer 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) at 1 mmol/L was included in the demembranation-reactivation medium, and free calcium ion activities were calibrated using the fluorescent calcium probe Fura-2. Calcium ion activities of > or =500 nmol/L significantly inhibited the percentage of demembranated-reactivated spermatozoa that were motile, and the velocity and lateral head displacement of these cells. The range of intracellular calcium activities in spermatozoa from 24 cryopreserved ejaculates was 110-534 nmol/L; roughly twice the value in fresh spermatozoa. Therefore, calcium ion activities in the range observed in cryopreserved spermatozoa can inhibit the activity of demembranated human spermatozoa.

Coumarin Substrates for Cytochrome P450 2D6 Fluorescence Assays

A set of nine 4-aminomethyl-7-alkoxycoumarin derivatives was synthesized and characterized as substrates for O-dealkylation by recombinant cytochrome P450 2D6, a major human enzyme involved in drug metabolism. Enzymatic O-dealkylation yields 7-hydroxycoumarins, which have useful fluorescence properties. The substrates, which differed in substitution at the amino and 7-hydroxy positions, varied in terms of catalytic efficiency of O-dealkylation and in their selectivity as substrates for cytochrome P450 2D6 in human liver microsomes. Several of the compounds are useful as cytochrome P450 2D6 substrates in single-phase, rapid-throughput assays.

Application of a high-performance liquid chromatographic assay for the neuromuscular blocker gallamine to analysis of rat plasma, muscle and microdialysate samples

A reliable high-performance liquid chromatographic method has been validated for determination of gallamine in rat plasma, muscle tissue and microdialysate samples. A C18 reversed-phase column with mobile phase of methanol and water containing 12.5 mM tetrabutyl ammonium (TBA) hydrogen sulphate (22:78, v/v) was used. The flow-rate was 1 ml/min with UV detection at 229 nm. Sample preparation involved protein precipitation with acetonitrile for plasma and muscle tissue homogenate samples. Microdialysate samples were injected into the HPLC system without any sample preparation. Intra-day and inter-day accuracy and precision of the assay were <13%. The limit of quantification was 1 microg/ml for plasma, 1.6 microg/g for muscle tissue and 0.5 microg/ml for microdialysate samples. The assay was applied successfully to analysis of samples obtained from a pharmacokinetic study in rats using the microdialysis technique.

Value of the hamster oocyte test and computerised measurements of sperm motility in predicting if four or more viable embryos will be obtained in an IVF cycle

The experimental group consisted of men from 81 couples waiting for in vitro fertilization (IVF), about half of whom had sperm dysfunction defined by a negative post-coital test. A diagnostic semen sample was subjected to a hamster oocyte penetration test (HOPT) after stimulation of the acrosome reaction with A23187 +/- pentoxifylline and to computerized sperm motility measurements (CASA) as well as conventional semen analysis according to the WHO protocol. Logistic regression was used to identify parameters that predicted the probability of achieving four or more viable embryos at IVF among the 65 couples from whom four or more oocytes were collected. The number of oocytes available and whether the woman had previously been pregnant (ever pregnant) were important factors but once these had been taken into account a number of sperm parameters had additional predictive power. The most useful of these were the percentage sperm static (CASA) or the percent sperm progressively motile (conventional semen analysis) in the Percoll preparation. A model incorporating the number of oocytes collected, ever pregnant and percentage sperm static achieved 85% correct prediction of outcome in the experimental dataset but only 62% correct prediction in an independent set of 280 IVF cycles. The percentage of hamster oocytes penetrated was a significant predictor but had no advantage over simple motility measurements. The results illustrate the difficulty of basing a prognosis for achieving satisfactory fertilization in IVF on the properties of spermatozoa.

Protein determination in cerebrospinal fluid by protein dye-binding assay

In this study, Coomassie brilliant blue (CBB) and pyrogallol red/molybdate (PRM) protein dye-binding assays for total protein determination in cerebrospinal fluid (CSF) are compared. Using human albumin (HA) as a protein calibrator, protein concentration in CSF samples (n = 73) ranged from 55-1960 mg/L (median: 315 mg/L) with the CBB assay, and from 95-2450 mg/L (median: 395 mg/L) with the PRM assay. Linear regression analysis indicated yCBB = 0.824xPRM - 8 (r = 0.99). The discrepancy between the values was investigated by comparing the response of the two assays to different proteins. Compared with HA, the PRM assay showed a more uniform response to human albumin/globulin (A/G) and bovine gamma globulin (G) than did the CBB assay, but it gave high colour yields with bovine myelin basic protein. When CSF was assayed using A/G as a protein calibrator, agreement between the methods improved (yCBB = 0.960xPRM + 0 [r = 0.99]), indicating that comparability is dictated by the choice of protein calibrator. Of the two assays studied, the PRM assay is recommended for CSF protein determination because it gives a more uniform and linear response to human albumin and globulin over a wider working range.

Protein concentration of cerebrospinal fluid by precipitation with Pyrogallol Red prior to sodium dodecyl sulphate-polyacrylamide gel electrophoresis

The Pyrogallol Red Molybdate (PRM) and Coomassie Brilliant Blue (CBB) protein dye-binding assays have been applied to samples of cerebrospinal fluid (CSF) to investigate protein concentration by dye precipitation prior to sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The protein concentration values of the CSF samples (N=62) showed good agreement between the PRM and CBB assays as indicated by linear regression analysis (y(PRM)=1.033x(CBB)+1.004 in units of mg/l, r=0.99) but the PRM assay was optimal for protein concentration as the PRM protein-dye complex was less soluble allowing protein recovery over a wider working range. Dye precipitation using PRM is recommended as a simple, rapid and economic method for protein concentration of samples of CSF prior to SDS-PAGE.

Imprinting structural information from a GpG ligand into the configuration of a chiral diamine ligand through second-sphere communication in platinum(II) complexes

Cisplatin forms the cis-Pt(NH3)2(d(GpG)) cross-link with DNA. We have recently created novel d(GpG) conformations by using "retro models" (complexes having bulky carrier ligands designed to slow d(GpG) dynamic motion). Our results define four conformer classes: HH1, HH2, delta HT1, and delta HT2, with a head-to-head or head-to-tail base orientation and a phosphodiester backbone with a normal (1) or opposite (2) propagation direction. Moreover, each G residue can be syn or anti, and the base canting can be left-handed (L) or right-handed (R). Thus, 32 variants of cis-Pt(NH3)2(d(GpG)) are conceivable, but the adduct is too dynamic to study. Thus far, by using retro models, we have obtained evidence for five variants with d(GpG) but only four with GpG. We therefore selected Me2DAPPt(GpG) complexes for study by 1H and 31P NMR spectroscopy, CD spectroscopy, and molecular mechanics and dynamics (MMD) calculations. Coordinated Me2DAP (N,N'-dimethyl-2,4-diaminopentane) has N, C, C, N chiral centers designated, for example, as R,R,R,R. This ligand has greater flexibility and more readily inverted N centers than ligands used previously in GpG retro models. One goal was to determine whether the GpG ligand can control the configuration of a carrier ligand. (R,R,R,R)-Me2DAPPt(GpG) forms the anti, anti HH1 R variant almost exclusively. Equal populations of the two possible linkage isomers of (S,R,R,R)-Me2DAPPt(GpG) are formed, both favoring the anti, anti HH1 R, variant; however, the isomer with the 5'-G cis to the S nitrogen has sharper signals, suggesting that interligand interactions are more favorable. Indeed, this linkage isomer was the major product of isomerization when (R,R,R,R)-Me2DAPPt(GpG) was kept at pH approximately 9.5 to allow N center equilibration. Steric clashes between the Me2DAP C-Me groups and the G O6 atoms found by MMD calculations appear to disfavor the HH1 conformer of (S,S,S,S)-Me2DAPPt(GpG) and (S,S,S,R)-Me2DAPPt(GpG) complexes. These two complexes have a significant population of the anti, syn delta HT1 conformer, as indicated by broad 1H NMR signals and by 31P NMR and CD data. Equilibration of (S,S,S,R)-Me2DAPPt(GpG) at pH 9.5 leads to a mixture of (S,S,S,S)-Me2DAPPt(GpG) and at least one isomer of (S,S,S,R)-Me2DAPPt(GpG). Thus, second-sphere communication (hydrogen bonding and steric interligand interactions) influences both GpG conformation and Me2DAP configuration.

Assessment of in vitro and in vivo recovery of gallamine using microdialysis

The application of microdialysis technique for the investigation of pharmacokinetics and pharmacodynamics of drugs requires careful assessment of probe performance to ensure validity of the data obtained using this technique. The aim of this study was to establish and validate the microdialysis technique for investigation of the pharmacokinetics and pharmacodynamics of the neuromuscular blocker, gallamine. In vitro recovery of gallamine from the microdialysis probe when different perfusion flow rates were employed was evaluated leading to selection of a flow rate of 2 microl/min with 15-min sampling intervals for the subsequent studies. In vitro recovery of gallamine from the microdialysis probe was independent of concentration, stable over an 8-h period and reproducible. Comparable in vitro recoveries were obtained by different established approaches including recovery estimation by gain, loss and the zero-net flux (ZNF) method. Recovery by loss was used to study the in vivo recovery of gallamine from rat muscle tissue. The in vivo recovery was stable over a 5.5-h sampling period. In vitro performance of the probe subsequent to the in vivo study remained stable supporting reusage of the probe. These data highlight the importance of a systematic examination of microdialysis probe validation.

Evidence that the NH2 terminus of vph1p, an integral subunit of the V0 sector of the yeast V-ATPase, interacts directly with the Vma1p and Vma13p subunits of the V1 sector

The vacuolar-type H(+)-ATPase (V-ATPase) is composed of a peripherally bound (V(1)) and a membrane-associated (V(0)) complex. V(1) ATP hydrolysis is thought to rotate a central stalk, which in turn, is hypothesized to drive V(0) proton translocation. Transduction of torque exerted by the rotating stalk on V(0) requires a fixed structural link (stator) between the complexes to prevent energy loss through futile rotation of V(1) relative to V(0); this work sought to identify stator components. The 95-kDa V-ATPase subunit, Vph1p, has a cytosolic NH(2) terminus (Nt-Vph1p) and a membrane-associated COOH terminus. Two-hybrid assays demonstrated that Nt-Vph1p interacts with the catalytic V(1) subunit, Vma1p. Co-immunoprecipitation of Vma1p with Nt-Vph1p confirmed the interaction. Expression of Nt-Vph1p in a Deltavph1 mutant was necessary to recruit Vma13p to V(1). Vma13p bound to Nt-Vph1p in vitro demonstrating direct interaction. Limited trypsin digests cleaves both Nt-Vph1p and Vma13p. The same tryptic treatment results in a loss of proton translocation while not reducing bafilomycin A(1)-sensitive ATP hydrolysis. Trypsin cleaved Vph1p at arginine 53. Elimination of the tryptic cleavage site by substitution of arginine 53 to serine partially protected vacuolar acidification from trypsin digestion. These results suggest that Vph1p may function as a component of a fixed structural link, or stator, coupling V(1) ATP hydrolysis to V(0) proton translocation.

Identification of murine B-cell and T-cell epitopes of Escherichia coli outer membrane protein F with synthetic polypeptides

The major pore-forming outer membrane proteins (Omps) of gram-negative bacteria demonstrate numerous immunomodulating properties and are involved in the virulence of pathogenic strains. Because Escherichia coli OmpF is the best-characterized porin in terms of structural and functional characteristics, in vitro B-cell and T-cell responses to this porin in six different strains of mice were analyzed. Mice were immunized with purified OmpF trimers or overlapping synthetic polypeptides (20-mers) spanning the entire 340-amino-acid sequence of the OmpF monomer. T-cell proliferative responses and immunoglobulin G antibody responses to native OmpF and the peptide analogues were determined. For each strain, patterns of T-cell proliferation were similar regardless of whether native OmpF or synthetic peptides were inoculated, although all strains recognized one or more cryptic determinants. Mice exhibited several haplotype-specific responses, but genetically permissive epitopes were also identified. Four peptides (75-94, 265-284, 295-314, and 305-324) elicited strong T-cell proliferative responses from all strains of mice when mice were presensitized with native OmpF or a homologous peptide. In general, 10 or fewer peptides were recognized by sera from mice immunized with native OmpF or synthetic peptides, and most sera from peptide-immunized mice reacted poorly with the native protein. Four peptides spanning amino acids 45 to 64, 95 to 114, 115 to 134, and 275 to 294 were recognized by sera from all strains immunized with native OmpF but not by sera from peptide-immunized mice. Peptides 245-264 and 305-324 were universally recognized by sera from peptide-immunized mice, but these sera reacted weakly or were negative when tested against the native protein. Based on the pattern of cytokine secretion by proliferating T cells, immunization with native OmpF polarizes T helper cells toward development of a TH1 response. T-cell and B-cell responses have been investigated based on the assumption that differences in epitope specificity could influence protective or pathologic host reactions. Because of the high level of structural homology of OmpF to porins isolated from other enteric pathogens, the identification of T- and B-cell-stimulatory determinants of E. coli OmpF may have broader application.

Clinical pharmacokinetics and pharmacodynamics of celecoxib: a selective cyclo-oxygenase-2 inhibitor

Celecoxib, a nonsteroidal anti-inflammatory drug (NSAID), is the first specific inhibitor of cyclo-oxygenase-2 (COX-2) approved to treat patients with rheumatism and osteoarthritis. Preliminary data suggest that celecoxib also has analgesic and anticancer properties. The selective inhibition of COX-2 is thought to lead to a reduction in the unwanted effects of NSAIDs. Upper gastrointestinal complication rates in clinical trials are significantly lower for celecoxib than for traditional nonselective NSAIDs (e.g. naproxen, ibuprofen and diclofenac). The rate of absorption of celexocib is moderate when given orally (peak plasma drug concentration occurs after 2 to 4 hours), although the extent of absorption is not known. Celexocib is extensively protein bound, primarily to plasma albumin, and has an apparent volume of distribution of 455+/-166L in humans. The area under the plasma concentration-time curve (AUC) of celecoxib increases in proportion to increasing oral doses between 100 and 800mg. Celecoxib is eliminated following biotransformation to carboxylic acid and glucuronide metabolites that are excreted in urine and faeces, with little drug (2%) being eliminated unchanged in the urine. Celecoxib is metabolised primarily by the cytochrome P450 (CYP) 2C9 isoenzyme and has an elimination half-life of about 11 hours in healthy individuals. Racial differences in drug disposition and pharmacokinetic changes in the elderly have been reported for celecoxib. Plasma concentrations (AUC) of celecoxib appear to be 43% lower in patients with chronic renal insufficiency [glomerular filtration rate 2.1 to 3.6 L/h (35 to 60 ml/min)] compared with individuals with healthy renal function, with a 47% increase in apparent clearance. Compared with healthy controls, it has been reported that the steady-state AUC is increased by approximately 40% and 180% in patients with mild and moderate hepatic impairment, respectively. Celecoxib does not appear to interact with warfarin, ketoconazole or methotrexate; however, clinically significant drug interactions with fluconazole and lithium have been documented. As celecoxib is metabolised by CYP2C9, increased clinical vigilance is required during the coadministration of other substrates or inhibitors of this enzyme.

Total protein determination in urine: elimination of a differential response between the coomassie blue and pyrogallol red protein dye-binding assays

BACKGROUND

The total protein content of urine is a good index of renal function, but its determination is unreliable. Protein dye-binding assays are simple, but they characteristically lack a uniform response to different proteins.

METHODS

We investigated a differential response of the Sigma Microprotein Coomassie Brilliant Blue (CBB) and Pyrogallol Red-molybdate (PRM) protein dye-binding assays to urine, using human albumin, albumin/globulin, or urinary protein as calibrator.

RESULTS

The urine protein values (n = 60) obtained with the CBB assay were 110-13 500 mg/L (mean, 2390 mg/L) compared with 160-18 300 mg/L (mean, 3470 mg/L) obtained with the PRM assay (CBB:PRM protein concentration ratio, 0.46-0.88, mean, 0. 69 +/- 0.10). The differential response was highly reproducible as indicated by Sigma urine control Level 1 (within-day CBB:PRM ratio, 0.68 +/- 0.02; between-day CBB:PRM ratio, 0.67 +/- 0.04) and Sigma urine control Level 2 (within-day CBB:PRM ratio, 0.60 +/- 0.01; between-day CBB:PRM ratio, 0.59 +/- 0.02). The use of urinary protein as a calibrator (rather than human albumin) greatly improved the agreement between the assays when applied to urine (y(CBB) = 0. 972x(PRM) - 16 vs y(CBB) = 0.685x(PRM) + 17). In studies using urine controls, this calibrator also improved agreement between the CBB, PRM, trichloroacetic acid (TCA), and benzethonium chloride protein methods and, to a lesser extent, agreement with the TCA-Ponceau S method.

CONCLUSION

The use of a urinary protein calibrator improves the agreement between different methods used to determine total protein in urine.

The protein composition of ferret parotid saliva as revealed by high-resolution electrophoretic methods

Ferret parotid saliva has been analysed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and two-dimensional electrophoresis (2-DE) to determine, for the first time, its protein composition. SDS-PAGE, in combination with Coomassie Brilliant Blue (CBB) staining, revealed up to 20 bands and the patterns were characterised by major protein constituents of Mr 105000, 51000, 47000, 33000, 22000 and 16 400 common to all samples from all animals. Sequential samples collected from the same animal during prolonged stimulation of the parasympathetic nerve (40 min at 40 Hz) showed subtle but reproducible protein changes. Saliva collected from different animals varied widely in the amount of a protein Mr 66000. 2-DE, in combination with silver staining, revealed up to 300 spots and the patterns were characterised by major protein constituents of Mr 105000 (pI 6.3-7.2), Mr 66000 (pI 4.7-5.3), Mr 51000 (pI 5.0-5.7), Mr 47000 (pI 6.0-7.5), and Mr 33000 (pI 4.7-6.0). Many of the polypeptide spot clusters consisted of one or more horizontal strings of spots suggesting extensive microheterogeneity. Both SDS-PAGE and 2-DE indicated that the protein patterns of ferret parotid saliva evoked by electrical stimulation of the parasympathetic nerve in the absence or presence of atropine are similar, i.e., the protein composition of the atropine-resistant nonadrenergic, noncholinergic (NANC) secretion is similar to that of saliva evoked in the absence of muscarinic receptor blockade.

Epidemiological patterns of musculoskeletal injuries and physical training

PURPOSE

The purpose of this study was to identify rates of diagnosis-specific musculoskeletal injuries in U.S. Marine Corps recruits and to examine the association between patterns of physical training and these injuries.

METHODS

Subjects were 1,296 randomly selected male Marine recruits, ages 17 to 28 yr, who reported to Marine Corps Recruit Depot San Diego for boot camp training between January 12 and September 14, 1993. Recruits were followed prospectively through 12 wk of training for injury outcomes. Injury patterns were examined in relation to weekly volumes and types of vigorous physical training.

RESULTS

The overall injury rate was 39.6% (number of recruits injured/population at risk), with 82% of injuries occurring in the lower extremities. Overuse injuries accounted for 78% of the diagnoses. The most frequent site of injury was the ankle/foot region (34.3% of injuries), followed by the knee (28.1%). Ankle sprains (6.2%, N = 1,143), iliotibial band syndrome (5.3%, N = 1,143), and stress fractures (4.0%, N = 1,296) were the most common diagnoses. Injury rates were highest during the weeks with high total volumes of vigorous physical training and the most hours of running and marching. Weekly injury rates were significantly correlated with hours of vigorous physical training (overuse injuries r = 0.667, P = 0.018; acute injuries r = 0.633, P = 0.027).

CONCLUSIONS

The results of this controlled epidemiological investigation indicate that volume of vigorous physical training may be an etiologic factor for exercise-related injuries. The findings also suggest that type of training, particularly running, and abrupt increases in training volume may further contribute to injury risk.

Reactive oxygen species (ROS) production and the outcome of diagnostic tests of sperm function

Washed sperm suspensions from 64 out of 89 (72%) randomly selected infertility patients produced detectable reactive oxygen species (ROS) compared to 17 out of 67 (25%) prospective semen donors (p < 0.01, Chi-square test). Among patients, the median sperm concentration in ejaculates which yielded sperm suspensions that generated detectable levels of ROS was lower than in those which did not: 36.2 (15.63-57.64) vs. 71.5 (22-108) x 10(6)/mL, respectively (median (interquartile range), p < 0.05, Kruskal-Wallis test). In samples that produced ROS, the basal rate of production and the rates after stimulation with 50 mumol N-formyl met leu phe (N-FMLP) l-1 or with 100 nmol phorbol 12-myristate 13-acetate (PMA) l-1 were significantly and inversely correlated with sperm concentration in the ejaculate (r = -0.43, -0.41 and -0.35, respectively, p < 0.01 Spearman's rank correlation). The rate of ROS production showed no relationship to the motility of spermatozoa in semen, whether evaluated visually or via computer assisted semen analysis. However, there was a significant negative correlation (r = -0.370) between the motile, normal sperm concentration (MNSC) and basal ROS production, and when stimulated with N-FMLP (r = -0.311) or with PMA (r = -0.249) (all p < 0.05). In patient samples that generated detectable ROS, the ability of the spermatozoa to retain motility for 24 h after preparation on a 40/80% Percoll gradient was negatively correlated with basal ROS production (r = -0.310, p < 0.05). ROS production was also related to the outcome of in vitro sperm mucus penetration tests. Unstimulated levels of ROS production showed a significant (p < 0.05), negative correlation with the number of progressively motile spermatozoa present in mucus after 15 (r = -0.379) and 60 (r = -0.362) min. These results suggest that sperm samples with increased ROS tend to have poor semen quality and reduced performance in a number of routine, diagnostic sperm function tests.

High-resolution electrophoretic analysis of rat parotid salivary proteins

Silver staining and high-resolution electrophoretic methods have been used to compare the protein composition of rat parotid saliva evoked in response to (i) parasympathetic stimulation (including the nonadrenergic, noncholinergic, atropine-associated secretion), (ii) sympathetic stimulation, or (iii) the infusion of neuropeptides with secretagogue activity (substance P, calcitonin gene-related peptide, neuropeptide Y, or vasoactive intestinal peptide). The different stimuli influenced the protein concentration and flow rate of the evoked secretion but had little effect upon the protein composition of the saliva. In contrast to earlier studies using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Coomassie blue staining, the combination of silver staining and two-dimensional electrophoresis (2-DE) revealed many newly detected proteins. The results indicate that the protein composition of rat parotid saliva is more complex than previously reported but is unaffected by the mode of stimulation.

Electrophoretic analysis of Bence Jones proteinuria

The electrophoresis of Bence Jones proteinuria (BJP) by urinary protein electrophoresis (UPE), immunoelectrophoresis (IE), immunofixation electrophoresis (IFE), sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), isoelectric focusing (IEF), two-dimensional electrophoresis (2-DE) and capillary electrophoresis (CE) is described. UPE, IE and IFE are briefly discussed as clinical laboratory methods for the detection and typing of free light chain (LC) whilst the high resolution electrophoretic methods (SDS-PAGE, IEF, 2-DE and CE) are considered in greater detail as research tools for molecular characterisation of free LC and its association with nephrotoxicity. Refinements of sample processing designed to improve the standardisation of analysis of BJP by high resolution electrophoretic methods are reported.

Stereoselective and substrate-dependent inhibition of hepatic mitochondria beta-oxidation and oxidative phosphorylation by the non-steroidal anti-inflammatory drugs ibuprofen, flurbiprofen, and ketorolac

Non-steroidal anti-inflammatory drugs (NSAIDs) cause a range of adverse effects, some of which have been associated with perturbances of lipid metabolic pathways. Previous data demonstrating stereoselective formation of the CoA thioester of R-ibuprofen in particular were suggestive of possible stereoselective effects on lipid metabolism. Our aim was to characterise the relative stereoselectivity of the effects of ibuprofen, flurbiprofen, and ketorolac (0.01-1.0 mM) on both the beta-oxidation of palmitate and oxidative phosphorylation in rat hepatic mitochondria as a means of dissecting prostaglandin related from non-prostaglandin-related events. Beta-oxidation was inhibited stereoselectively by R-ibuprofen (P = 0.015), non-stereoselectively by R- and S-flurbiprofen (P = 0.002 and P = 0.004, respectively), and was essentially unaffected by either enantiomer of ketorolac. At 0.25 mM, inhibition by R-ibuprofen and both flurbiprofen enantiomers was partially reversed by increasing CoA concentrations (0-200 microM). Mitochondrial respiration was moderately inhibited by both enantiomers of ibuprofen and flurbiprofen (P < 0.01), but only by high concentrations (> or = 1 mM) of the enantiomers of ketorolac (P < 0.01). Uncoupling of oxidative phosphorylation measured as stimulation of State 4 respiration contributed to these effects. The data support interactions involving both stereoselective CoA-dependent and non-CoA-dependent mechanisms. The plasma drug concentrations required to achieve these effects are not likely to be attained in the majority of patients, although these concentrations are achievable in the gastrointestinal tract and may contribute to the well-known spectrum of adverse effects in this organ. Some patients do experience systemic adverse events which may be mediated by these mechanisms.

Pharmacokinetics of nonsteroidal anti-inflammatory drugs in synovial fluid

The major site of action for nonsteroidal anti-inflammatory drugs (NSAIDs) in the treatment of rheumatic diseases is probably within the synovial compartment. There has been little work on the disposition of NSAIDs in the synovium and most studies have involved the measurement of their concentrations in synovial fluid. The concentrations of NSAIDs are more sustained in synovial fluid than in plasma, the difference being particularly noted with NSAIDs with short elimination half-lives. The more sustained concentrations may contribute to the prolonged effect of the short half-life NSAIDs, which are usually administered at intervals longer than their half-lives in plasma. The most widely used method of kinetic analysis of NSAIDs in synovial fluid is a compartmental model in which synovial fluid is a peripheral compartment of distribution of the drug. Repeated samples of synovial fluid from individual patients are difficult to collect, but even 1 sample of synovial fluid and plasma from each patient can provide useful data when analysed using the population approach to pharmacokinetic analysis. According to the compartmental model, the mean half-lives of efflux of the NSAIDs from synovial fluid range from 1.5 to 7 hours. The mean partition coefficient of most NSAIDs between synovial fluid and plasma is approximately 0.6. The NSAIDs are highly protein-bound, and the lower mean concentrations in synovial fluid are largely because of the lower concentrations of the binding protein, albumin. The NSAIDs diffuse into and out of synovial fluid in their unbound forms, but there is some diffusion in the protein-bound forms, particularly out of synovial fluid. The mean rates of diffusion of NSAIDs into and out of skin blisters in humans are similar to the rates of influx and efflux in the synovial fluid of the knee, but there is considerable variation between the pharmacokinetics of transfer at the 2 sites in individual patients. NSAIDs decrease the synthesis of prostaglandins in synovial fluid, but there are few data on the relationship between the kinetics of NSAIDs in synovial fluid and the effects on prostaglandin synthesis.

Use of simple measures of physical activity to predict stress fractures in young men undergoing a rigorous physical training program

Among a population of randomly selected US Marine Corps recruits at Marine Corps Recruit Depot, San Diego, California, the authors developed a screening tool to identify individuals at high risk for lower extremity stress fracture when beginning a rigorous physical training program. The screening tool was developed among 1,286 recruits, then tested and refined among 1,078 additional recruits. The refined algorithm, consisting of five physical activity questions and a 1.5-mi (2.4-km) run time, revealed that 21.6% of "high risk" subjects suffered more than three times as many stress fractures as "low risk" subjects. These data suggest that risk of stress fracture during rigorous physical training is increased by poor physical fitness and low levels of physical activity prior to their entry into the program.

Therapeutic drug monitoring: antiarrhythmic drugs

Antiarrhythmic agents are traditionally classified according to Vaughan Williams into four classes of action. Class I antiarrhythmic agents include most of the drugs traditionally thought of as antiarrhythmics, and have as a common action, blockade of the fast-inward sodium channel on myocardium. These agents have a very significant toxicity, and while they are being used less, therapeutic drug monitoring (TDM) does significantly increase the safety with which they can be administered. Class II agents are antisympathetic drugs, particularly the beta-adrenoceptor blockers. These are generally safe agents which do not normally require TDM. Class III antiarrhythmic agents include sotalol and amiodarone. TDM can be useful in the case of amiodarone to monitor compliance and toxicity but is generally of little value for sotalol. Class IV antiarrhythmic drugs are the calcium channel blockers verapamil and diltiazem. These are normally monitored by haemodynamic effects, rather than using TDM. Other agents which do not fall neatly into the Vaughan Williams classification include digoxin and perhexiline. TDM is very useful for monitoring the administration (and particularly the safety) of both of these agents.

Effect of clofibrate on the chiral inversion of ibuprofen in healthy volunteers

OBJECTIVES

To determine the influence of the hypolipidemic drug clofibrate on the stereoselective metabolism of ibuprofen in humans.

METHODS

Healthy male subjects (n = 12) ingested a dose of 400 mg pseudoracemic ibuprofen (200 mg R-ibuprofen, 160 mg S-ibuprofen, and 40 mg 13C-S-ibuprofen) on two occasions after either pretreatment with clofibrate (2 gm/day over 1 week) or no pretreatment in a randomized order.

RESULTS

When subjects were pretreated with clofibrate, clearances of R-ibuprofen and 13C-S-ibuprofen increased significantly from 55.0 and 66.4 ml/min to 186.2 and 106.7 ml/min (p < 0.01), respectively. This increase was similarly reflected in the clearance by inversion of R-ibuprofen (control, 36.0 ml/min; treated, 118.8 ml/min; p < 0.01), as well as in the clearance by noninversion (control, 19.0 ml/min; treated, 67.4 ml/min; p < 0.01). Unbound clearance values significantly increased for R-ibuprofen (control, 19.5 L/min; treated, 38.7 L/min) but not for 13C-S-ibuprofen (11.8 versus 10.6 L/min, respectively). The fractional inversion of ibuprofen calculated from the urinary metabolite data was increased after clofibrate pretreatment (clofibrate group, 66.4%; control, 53.5%; p < 0.01). However, this was not evident when fractional inversion was calculated from the plasma concentration-time data for the unmetabolized drug.

CONCLUSIONS

Clofibrate altered the stereoselective disposition of ibuprofen in healthy volunteers by increased formation of R-ibuprofenoyl-coenzyme A rather than by an effect on oxidative metabolism of ibuprofen. This interaction has potential therapeutic implications.