Metabolite ratios

Considerable investigative effort has been directed to the role of metabolite ratios and multiple metabolites in enzymic control. The complex nature of such control is exemplified by studies of oscillatory responses in the glycolytic pathway in both intact yeast cells and bovine heart cytosol. This subject has been considered by Higgins (1967), Hess and Boiteux (1971), Walter (1972, 1974), and Goldbeter and Caplan (1976) and is discussed in Chapter 8 of this volume. 

Regulation by variation of the adenine nucleotide pool or the NAD/ NADH ratio appears to be of particular physiologic import, since the adenylate nucleotides represent the principal storage form of chemical energy, while the pyridine nucleotides are the major source of reducing potential in the cell. With the two pools linked via electron transport and oxidative phosphorylation, any perturbation which affects either of the pools may have wide-ranging consequences on diverse reactions 

The NAD/NADH couple, as the major source of reducing potential, occupies a position of preeminence akin to that of the adenine nucleotides. Dehydrogenase, catalyzing freely reversible reactions, (e.g., alcohol and lactate dehydrogenases), are subject to rate and direction control by the NAD/NADH ratio. Williamson et al. (1967) proposed a means of determining the NAD/NADH ratio in various intracellular compartments by measuring substrate/product ratios in freeze-clamped tissues that have dehydrogenases that catalyze a reaction at or near 

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Oesterheld, J. Kallepalli, B. R. (1997). Grapefruit juice and clomipramine shifting metabolitic ratios./. Clin. Psychopharmacol, 17(1), 62-3. 

Dempsey D, Jacob P, 3rd, Benowitz NL (2002) Accelerated metabolism of nicotine and cotinine in pregnant smokers. J Pharmacol Exp Ther 301(2) 594-598 Dempsey D, Tutka P, Jacob P, 3rd, Allen F, Schoedel K, Tyndale RF, Benowitz NL (2004) Nicotine metabolite ratio as an index of cytochrome P450 2A6 metabolic activity. Clin Pharmacol Ther 76 64-72... 

Lerman C, Tyndale R, Patterson F, Wileyto EP, Shields PG, Pinto A, Benowitz N (2006) Nicotine metabolite ratio predicts efiScacy of transdermal nicotine for smoking cessation, Clin Pharmacol Ther79(6) 600-608... 

In milk, the concentration of SDM and its metabolites was a reflection of those in plasma (14 Figure 4). The disposition of SDM in plasma, edible tissues, bile and urine of calves are illustrated in Figure 5. As shown, the SDM concentration in plasma was higher than that in the edible tissues. The latter is also confirmed by the tissue to plasma concentration ratios of SDM and its metabolites which were lower than 1, except for the metabolite ratios in kidney tissue (Table II). The SCH2OH concentration in the kidney exceeded those of SDM (Figure 6). The N -SDM metabolite concentrations in muscle, kidney and liver were always below those of SDM (Table II ... 

N-demethylase activity was monitored by the CBT, and 7-N-demethylase activity was monitored by the caffeine urinary metabolite ratio (CMR). PBB-exposed subjects had higher CBT values (p<0.02) than urban nonsmokers, but tire values were comparable to those of urban smokers. The correlation between serum PBB levels and the CBT value was poor (r ().2). The CMR value in PBB-exposed subjects was also higher than that of urban nonsmokers (p<0.05) there was no correlation between serum PBB levels and CMR values. Generally, smokers have higher CBT values than nonsmokers due to the presence of polycyclic aromatic hydrocarbons (PAH) in tobacco smoke, which induce CYPIA (Kotake et al. 1982). 

Lambert GH, Schoeller DA, Humphrey HEB, et al. 1990. The caffeine breath test and caffeine urinary metabolite ratios in the Michigan cohort exposed to polybrominated biphenyls A preliminary study. Environ Health Perspect 89 175-181. 

Bechtold, W.E., Strunk, M.R., Chang, I.-Y., Ward, J.B., Jr Henderson. R.F. (1994) Species differences in urinary butadiene metabolites comparisons of metabolite ratios between mice, rats and humans. Toxicol, appl. Pharmacol.,. Tl, 44-49... 

In contrast, data from a recent conference presentation by Choc and Robinson [100], indicated that cyclosporin metabolite ratios were similar after oral administration of either Sandimmun or the Neoral formulation, suggesting minimal changes in cyclosporin first-pass metabolism after Neoral administration. Furthermore, Neoral/Sandimmun area under the curve (AUC) ratios were similar (approximately 2) after cyclosporin administration in either the absence or presence of a CYP3A/P-gp inhibitor, whereas an AUC ratio of approximately 1 would have been expected if bioavailability was limited by metabolism or antitransport. However, these data have not yet been published, and the relative contributions of enhanced absorption or reduced metabolism in the CY bioavailability enhancement provided by Sandimmun Neoral are yet to be fully defined. 

The metabolite ratio, defined as the ratio of AUCo-oo of the metabolite to that of the parent, is a measure of the relative exposure of the metabolite to that of the parent, and could only be computed on 19 observations. The metabolite ratio for ILX651-C-carboxylate was not affected by dose, BSA, or day of administration, and was estimated at 0.59, indicating that the metabolite had about 59% the exposure of the parent. Hence, about one-third the total exposure (parent + metabolite) was due to the metabolite. This conclusion must be tempered, however, as few observations were made at the lower doses due to an inability to estimate AUC0, . 

Kalow W, Tang BK. Use of caffeine metabolite ratios to explore CYP1A2 and xanthine oxidase activities. Clin Pharmacol Ther 1991 50 508-519. 

Grogan J, Shou M, Zhou D, et al. Use of aromatase (CYP19) metabolite ratios to characterize electron transfer from NADPH-cytochrome P450 reductase. Biochemistry 1993 32(45) 12007-12012. 

Campbell ME, Speilberg SP, Kalow W. A urinary metabolite ratio that reflects systemic caffeine clearance. Clin Pharmacol Ther 1987 42 157-165. 

Rost KL, Roots I. Accelerated caffeine metabolism after omeprazole treatment as indicated by urinary metabolite ratios coincidence with plasma clearance and breath test. Clin Pharmacol Ther 1994 55 402 111. 

Table 1 Common Caffeine Urinary Metabolite Ratios Used as Phenotypic Measures of CYP1A2 Activity...

Rostami-Hodjegan A, Nurminen S, Jackson PR, et al. Caffeine urinary metabolite ratios as markers of enzyme activity a theoretical assessment. Pharmacogenetics 1996 6 121 149. 

Denaro CP, Wilson M, Jacob P El, et al. Validation of urine caffeine metabolite ratios with use of stable isotope-labeled caffeine clearance. Clin Pharmacol Ther... 

Simultaneous administration of a mixture of substrates of CYP enzymes in one study (i.e., a cocktail approach ) in human volunteers is another way to valuate a drug s inhibition or induction potential (35), provided that the study is designed properly and the following factors are present (1) the substrates are specific for individual CYP enzymes, (2) there are no interactions among these substrates, and (3) the study is conducted in a sufficient number of subjects. Negative results from a cocktail study can eliminate the need for further evaluation of particular CYP enzymes. However, positive results can indicate the need for further in vivo evaluation to provide quantitative exposure changes (such as AUC and Cmax), if the initial evaluation only assessed the changes in the urinary parent to metabolite ratios. 

Han XM, Ou-Yang DS, Lu PX et al. (2001) Plasma caffeine metabolite ratio (17X/137X) in vivo associated with G-2964A and C734A polymorphisms of human CYP1A2. Pharmacogenetics 11 429-435... 

Losartan (25 mg dose) has been proposed as a safer alternative to tolbutamide. The determination of losartan/E3174(oxidized metabolite) ratio in 0-8 hour urine or in plasma at 6 hours post dosing have been proposed (Yasar 2002 Sekino 2003). However, in a comparative study in sixteen subjects, a better correlation between genotyping and phenotyping was found with tolbutamide, as compared to losartan or flurbiprofen, though there was no subject with the C9 2/ 3 or C9 3/ 3 variants (Lee 2003). 

Nyeki A, Buclin T, Biollaz J, Decosterd LA (2002) NAT2 and CYP1A2 phenotyping with caffeine head-to-head comparison of AFMU vs. AAMU in the urine metabolite ratios. Br J Clin Pharmacol 55 62-67... 

At present, no blood markers are commonly used as indicators of niacin status. Most assessments of niacin nutriture have been based on measurement of the 2 urinary metabolites, N -methylnicotinamide and N -methyl-2-pyridone-5-carboxamide. Normally, adults excrete 20% to 30% of their niacin in the form of methylnicotinamide and 40% to 60% as the pyridone. An excretion ratio of pyridone to methylnicotinamide of 1.3 to 4.0 is thus normal, but latent niacin deficiency is indicated by a value below 1.0. As depletion occurs, the pyridone is absent for weeks before clinical signs are noted, and the methylnicotinamide excretion falls to a minimum at about the time that clinical signs are evident.f HPLC methods are currently the methods of choice, though some capillary electrophoresis methods have been developed. However, the measurement of 2-pyridone and N -methylnicotinamide concentrations in plasma may provide a more reliable metabolite ratio than urine measurements. A newer approach that may prove valuable is the ratio of NAD/NADP in erythrocytes and plasma tryptophan. A ratio of NAD/NADP below 1.0 would be indicative of a risk of developing niacin deficiency. ... 

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