Scientific inveStigAtionS introduction:Obstructive sleep apnea (OSA) is widely accepted to improve during slow wave sleep (SWS) compared to lighter stages of NREM sleep. However, supporting data to establish the magnitude and prevalence of this effect is lacking. Consequently, we examined this phenomenon, controlling for posture, in a large group of patients investigated for OSA at an academic clinical sleep service. Methods: A detailed retrospective analysis was conducted on data obtained from each 30-sec epoch of sleep in 253 consecutive fullnight diagnostic polysomnography studies performed over a 3-month period. Respiratory and arousal event rates were calculated within each stage of sleep, in the supine and lateral postures, and across the whole night, with OSA patients classified on the basis of an overall apnea-hypopnea index (AHI) ≥ 15 events/h. Central sleep apnea (CSA) patients were defined by a central apnea index ≥ 5/h. Sleep latency and time, and respiratory and arousal event rates in OSA, CSA, and non-OSA patients were compared between sleep stages and postures using linear mixed model analysis. The numbers of patients achieving reduced event rates in SWS and in the lateral posture were also examined.Results: There were 171 patients with OSA, 14 with CSA, and 68 non-OSA patients. OSA patients took significantly longer to achieve slow wave and REM sleep (p < 0.001) than non-OSA patients and had less stage 4 sleep (p = 0.037). There were striking improvements in AHI and arousal index (AI) from stage 1 to 4 NREM sleep (p < 0.001), with intermediate levels in REM sleep. AHI and AI were also markedly reduced in lateral versus supine sleep in all sleep stages (p < 0.001), with an effect size comparable to that of the slow wave sleep effect. The majority of OSA patients achieved low respiratory event rates in SWS. Eighty-two percent of patients achieved an AHI < 15 and 57% < 5 events/hour during stage 4 sleep. Conclusion:Although OSA patients demonstrate both a delayed and reduced proportion of SWS compared to non-OSA subjects, once they achieved SWS, AHI, and AI markedly improved in most patients.

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The human UDP glycosyltransferase (UGT) 3A family is one of three families involved in the metabolism of small lipophilic compounds. Members of these families catalyze the addition of sugar residues to chemicals, which enhances their excretion from the body. The UGT1 and UGT2 family members primarily use UDP glucuronic acid to glucuronidate numerous compounds, such as steroids, bile acids, and therapeutic drugs. We showed recently that UGT3A1, the first member of the UGT3 family to be characterized, is unusual in using UDP N-acetylglucosamine as sugar donor, rather than UDP glucuronic acid or other UDP sugar nucleotides (J Biol Chem 283:36205-36210, 2008). Here, we report the cloning, expression, and characterization of UGT3A2, the second member of the UGT3 family. Like UGT3A1, UGT3A2 is inactive with UDP glucuronic acid as sugar donor. However, in contrast to UGT3A1, UGT3A2 uses both UDP glucose and UDP xylose but not UDP N-acetylglucosamine to glycosidate a broad range of substrates including 4-methylumbelliferone, 1-hydroxypyrene, bioflavones, and estrogens. It has low activity toward bile acids and androgens. UGT3A2 transcripts are found in the thymus, testis, and kidney but are barely detectable in the liver and gastrointestinal tract. The low expression of UGT3A2 in the latter, which are the main organs of drug metabolism, suggests that UGT3A2 has a more selective role in protecting the organs in which it is expressed against toxic insult rather than a more generalized role in drug metabolism. The broad substrate and novel UDP sugar specificity of UGT3A2 would be advantageous for such a function.

AIMTo determine the scaling factors required for inclusion of renal drug glucuronidation clearance in the prediction of total clearance via glucuronidation (CL UGT ). METHODSMicrosomal protein per gram of kidney (MPPGK) was determined for human 'mixed' kidney (n = 5) microsomes (MKM). The glucuronidation activities of deferiprone (DEF), propofol (PRO) and zidovudine (AZT) by MKM and paired cortical (KCM) and medullary (KMM) microsomes were measured, along with the UGT 1A6, 1A9 and 2B7 protein contents of each enzyme source. Unbound intrinsic clearances (CL int,u,UGT ) for PRO and morphine (MOR; 3-and 6-) glucuronidation by MKM, human liver microsomes (HLM) and recombinant UGT1A9 and 2B7 were additionally determined. Data were scaled using in vitro-in vivo extrapolation (IV-IVE) approaches to assess the influence of renal CL int,u,UGT on the prediction accuracy of the calculated CL UGT values of PRO and MOR. RESULTSMPPGK was 9.3 ± 2.0 mg g À1 (mean ± SD). The respective rates of DEF (UGT1A6), PRO (UGT1A9) and AZT (UGT2B7) glucuronidation by KCM were 1.4-, 5.2-and 10.5-fold higher than those for KMM. UGT 1A6, 1A9 and 2B7 were the only enzymes expressed in kidney. Consistent with the activity data, the abundance of each of these enzymes was greater in KCM than in KMM. The abundance of UGT1A9 in MKM (61.3 pmol mg À1 ) was 2.7 fold higher than that reported for HLM. CONCLUSIONSScaled renal PRO glucuronidation CL int,u,UGT was double that of liver. Renal CL int,u,UGT should be accounted for in the IV-IVE of UGT1A9 and considered for UGT1A6 and 2B7 substrates. WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT• Multiple drugs, non-drug xenobiotics and endobiotics are glucuronidated by human kidney.• UDP-glucuronosyltransferase (UGT) 1A proteins and UGT2B7 are variably expressed in the tubule components of the human nephron. • Development of kidney specific in vitro-in vivo extrapolation (IV-IVE) approaches is hampered by the limited availability of microsomal protein per gram of kidney (MPPGK) and knowledge of the content and anatomic distribution of individual UGT enzymes. WHAT THIS STUDY ADDS• This study provides scaling factors to assess the relative contribution of the kidney to renal drug clearance via glucuronidation.• It demonstrates anatomic differences in renal glucuronidation activity and provides data on the contents of UGT1A6, UGT1A9 and UGT2B7 in human kidney cortex and medulla.• It establishes that UGT1A9 is 2.7-fold more abundant in human kidney microsomes than hepatic microsomes, indicating the need to include renal glucuronidation unbound intrinsic clearance in IV-IVE predictions for substrates glucuronidated by UGT1A9. IntroductionThe human kidney has an array of functions that include the regulation of blood osmolarity, volume, ionic composition and pH, the production of renin, 1,25-dihydroxyvitamin D, erythropoietin, prostaglandins and bradykinin, and the excretion of endogenous metabolites and xenobiotics. The cortex is characterized by the presence of glomeruli, tufts of capillaries and numerous convoluted ...

Morphine 3-b-D-glucuronide (M3G) and morphine 6-b-D-glucuronide (M6G) are the major metabolites of morphine in humans. More recently, morphine-3-b-D-glucoside (M-3-glucoside) was identified in the urine of patients treated with morphine. Kinetic and inhibition studies using human liver microsomes (HLM) and recombinant UGTs as enzyme sources along with molecular modeling were used here to characterize the relationship between morphine glucuronidation and glucosidation. The M3G to M6G intrinsic clearance (CL int ) ratio (∼5.5) from HLM supplemented with UDP-glucuronic acid (UDP-GlcUA) alone was consistent with the relative formation of these metabolites in humans. The mean CL int values observed for M-3-glucoside by incubations of HLM with UDP-glucose (UDP-Glc) as cofactor were approximately twice those for M6G formation. However, although the M3G-to-M6G CL int ratio remained close to 5.5 when human liver microsomal kinetic studies were performed in the presence of a 1: 1 mixture of cofactors, the mean CL int value for M-3-glucoside formation was less than that of M6G. Studies with UGT enzymeselective inhibitors and recombinant UGT enzymes, along with effects of BSA on morphine glycosidation kinetics, were consistent with a major role of UGT2B7 in both morphine glucuronidation and glucosidation. Molecular modeling identified key amino acids involved in the binding of UDP-GlcUA and UDP-Glc to UGT2B7. Mutagenesis of these residues abolished morphine glucuronidation and glucosidation. Overall, the data indicate that morphine glucuronidation and glucosidation occur as complementary metabolic pathways catalyzed by a common enzyme (UGT2B7). Glucuronidation is the dominant metabolic pathway because the binding affinity of UDP-GlcUA to UGT2B7 is higher than that of UDP-Glc.