The TMAO-Generating Enzyme Flavin Monooxygenase 3 Is a Central Regulator of Cholesterol Balance

Circulating levels of the gut microbe-derived metabolite trimethylamine-N-oxide (TMAO) have recently been linked to cardiovascular disease (CVD) risk. Here, we performed transcriptional profiling in mouse models of altered reverse cholesterol transport (RCT) and serendipitously identified the TMAO-generating enzyme flavin monooxygenase 3 (FMO3) as a powerful modifier of cholesterol metabolism and RCT. Knockdown of FMO3 in cholesterol-fed mice alters biliary lipid secretion, blunts intestinal cholesterol absorption, and limits the production of hepatic oxysterols and cholesteryl esters. Furthermore, FMO3 knockdown stimulates basal and liver X receptor (LXR)-stimulated macrophage RCT, thereby improving cholesterol balance. Conversely, FMO3 knockdown exacerbates hepatic endoplasmic reticulum (ER) stress and inflammation in part by decreasing hepatic oxysterol levels and subsequent LXR activation. FMO3 is thus identified as a central integrator of hepatic cholesterol and triacylglycerol metabolism, inflammation, and ER stress. These studies suggest that the gut microbiota-driven TMA/FMO3/TMAO pathway is a key regulator of lipid metabolism and inflammation.

Abstract 65: Flavin Monoxygenase 3 (FMO3) is a Novel Regulator of Hepatic Cholesterol Metabolism and Transintestinal Cholesterol Efflux (TICE)

Recent studies have revealed a novel route for cholesterol disposal through intestine known as transintestinal cholesterol efflux (TICE) that significantly contributes to fecal neutral sterol loss. This pathway is an integral part of reverse cholesterol transport (RCT), yet major mechanisms regulating TICE are not well understood. Using an unbiased transcriptional profiling approach in mouse models of augmented TICE, we found that hepatic expression of the enzyme Flavin monoxygenase 3 (FMO3) was dramatically repressed. At the same time we identified this enzyme through transcriptional profiling, it was reported that plasma levels of its product trimethylamineoxide (TMAO) are highly predictive of atheroslcerosis in humans, and TMAO is proatherogenic in mice. To further understand FMO3’s role as a regulator of cholesterol metabolism we used antisense oligonucleotides (ASO) to knockdown FMO3 expression in mouse liver in C57BL/6 mice fed either low (0.02%) or high (0.2%) levels of dietary cholesterol. As expected, FMO3 knockdown (>90% knockdown in the liver) increased the TMA/TMAO ratio in plasma more than 3-fold. Interestingly, knockdown of FMO biliary cholesterol levels were reduced by 60%, whereas fecal cholesterol loss was quite normal in FMO3 ASO treated mice fed a high cholesterol diet, which phenocopies a previously described mouse model where TICE predominates (NPC1L1-liver transgenic mice). ASO-mediated knockdown of FMO3 also unexpectedly reduced hepatic cholesteryl ester (CE) storage by 70% in mice fed 0.2% cholesterol. In parallel, knockdown of FMO3 reduces plasma VLDL cholesterol levels and the secretion rate of VLDL cholesteryl ester, but not triacylglycerol in cholesterol fed mice. FMO3 knockdown also reduced the hepatic expression of several liver X receptor (LXR) target genes, while increasing expression of genes involved in cholesterol synthesis. Collectively, these studies have identified FMO3 as a novel regulator of hepatic cholesterol metabolism and TICE. Given that plasma levels of FMO3’s product (TMAO) are strongly associated with atherosclerosis development in humans, and production of TMAO promotes atherosclerosis in mice, these studies have important implications for future cardiovascular drug discovery.

Intestinal SR-BI does not impact cholesterol absorption or transintestinal cholesterol efflux in mice

Reverse cholesterol transport (RCT) can proceed through the classic hepatobiliary route or through the nonbiliary transintestinal cholesterol efflux (TICE) pathway. Scavenger receptor class B type I (SR-BI) plays a critical role in the classic hepatobiliary route of RCT. However, the role of SR-BI in TICE has not been studied. To examine the role of intestinal SR-BI in TICE, sterol balance was measured in control mice and mice transgenically overexpressing SR-BI in the proximal small intestine (SR-BI(hApoCIII-ApoAIV-Tg)). SR-BI(hApoCIII-ApoAIV-Tg) mice had significantly lower plasma cholesterol levels compared with wild-type controls, yet SR-BI(hApoCIII-ApoAIV-Tg) mice had normal fractional cholesterol absorption and fecal neutral sterol excretion. Both in the absence or presence of ezetimibe, intestinal SR-BI overexpression had no impact on the amount of cholesterol excreted in the feces. To specifically study effects of intestinal SR-BI on TICE we crossed SR-BI(hApoCIII-ApoAIV-Tg) mice into a mouse model that preferentially utilized the TICE pathway for RCT (Niemann-Pick C1-like 1 liver transgenic), and likewise found no alterations in cholesterol absorption or fecal sterol excretion. Finally, mice lacking SR-BI in all tissues also exhibited normal cholesterol absorption and fecal cholesterol disposal. Collectively, these results suggest that SR-BI is not rate limiting for intestinal cholesterol absorption or for fecal neutral sterol loss through the TICE pathway.

Biliary sterol secretion is not required for macrophage reverse cholesterol transport

Recent evidence suggests that the intestine may play a direct facilitative role in reverse cholesterol transport (RCT), independent of hepatobiliary secretion. In order to understand the nonbiliary pathway for RCT, we created both genetic and surgical models of biliary cholesterol insufficiency. To genetically inhibit biliary cholesterol secretion, we generated mice in which Niemann-Pick C1-Like 1 (NPC1L1) was overexpressed in the liver. Compared to controls, NPC1L1(Liver-Tg) mice exhibit a >90% decrease in biliary cholesterol secretion, yet mass fecal sterol loss and macrophage RCT are normal. To surgically inhibit biliary emptying into the intestine, we have established an acute biliary diversion model. Strikingly, macrophage RCT persists in mice surgically lacking the ability to secrete bile into the intestine. Collectively, these studies demonstrate that mass fecal sterol loss and macrophage RCT can proceed in the absence of biliary sterol secretion, challenging the obligate role of bile in RCT.

Directed evolution of Aspergillus niger glucoamylase to increase thermostability

Using directed evolution and site-directed mutagenesis, we have isolated a highly thermostable variant of Aspergillus niger glucoamylase (GA), designated CR2-1. CR2-1 includes the previously described mutations Asn20Cys and Ala27Cys (forming a new disulfide bond), Ser30Pro, Thr62Ala, Ser119Pro, Gly137Ala, Thr290Ala, His391Tyr and Ser436Pro. In addition, CR2-1 includes several new putative thermostable mutations, Val59Ala, Val88Ile, Ser211Pro, Asp293Ala, Thr390Ser, Tyr402Phe and Glu408Lys, identified by directed evolution. CR2-1 GA has a catalytic efficiency (k(cat)/K(m)) at 35°C and a specific activity at 50°C similar to that of wild-type GA. Irreversible inactivation tests indicated that CR2-1 increases the free energy of thermoinactivation at 80°C by 10 kJ mol(-1) compared with that of wild-type GA. Thus, CR2-1 is more thermostable (by 5 kJ mol(-1) at 80°C) than the most thermostable A. niger GA variant previously described, THS8. In addition, Val59Ala and Glu408Lys were shown to individually increase the thermostability in GA variants by 1 and 2 kJ mol(-1), respectively, at 80°C.

TCDD-inducible poly(ADP-ribose) polymerase: a novel response to 2,3,7,8-tetrachlorodibenzo-p-dioxin

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) causes pleotropic effects in mammalian species through modulating gene expression. Here we analyzed TCDD-induced mRNA expression by using mRNA differential display and report the cloning of a novel TCDD-inducible poly(ADP-ribose) polymerase (TiPARP). TiPARP cDNA contains an open reading frame of 657 amino acid residues; the carboxyl half shares sequence similarity to the catalytic domain of PARP, a family of enzymes that catalyze poly ADP-ribosylation of proteins. Expression of the cDNA by in vitro transcription/translation reveals a protein of approximately 75 kDa. The expressed TiPARP exhibits PARP activity toward histone. TiPARP is highly homologous to RM1 which is induced during long-term potentiation, a memory formation process, and to TIL which is induced in T cells infiltrating progressing tumors. TiPARP mRNA is expressed in a broad range of mouse tissues. Together, these data demonstrate that TiPARP is a novel target of TCDD that may contribute to multiple responses to TCDD by modulating protein function through poly ADP-ribosylation.

A new tool for predicting erectile dysfunction

The Sexual Health Inventory for Men (SHIM) is an effective way to assess erectile difficulty (ED). Despite documented efficacy, however, many physicians may be reluctant to incorporate it into clinical practice because of the intimate nature of the questionnaire. In an attempt to devise and test an easy-to-use computer-based SHIM score indicator for office use, more than 30,000 SHIM questionnaires were administered to men visiting physicians' offices in 2000. Information about age, current smoking status, diabetes, depression, hypertension, prostate disease, and cholesterol levels was also collected. A logistic regression model with a sensitivity of 81.8% and a specificity of 57.7% was created to predict the likelihood of ED in a patient scoring below 21 (SHIM definition). This model was built into a highly graphic Windows-based program. The SHIM score indicator is a convenient way to rapidly identify patients at high risk for ED who should be further assessed.

The Missing Link: Early Methane ("T") Dwarfs in the Sloan Digital Sky Survey

We report the discovery of three cool brown dwarfs that fall in the effective temperature gap between the latest L dwarfs currently known, with no methane absorption bands in the 1-2.5 µm range, and the previously known methane (T) dwarfs, whose spectra are dominated by methane and water. The newly discovered objects were detected as very red objects in the Sloan Digital Sky Survey imaging data and have JHK colors between the red L dwarfs and the blue Gl 229B-like T dwarfs. They show both CO and CH(4) absorption in their near-infrared spectra in addition to H(2)O, with weaker CH(4) absorption features in the H and K bands than those in all other methane dwarfs reported to date. Due to the presence of CH(4) in these bands, we propose that these objects are early T dwarfs. The three form part of the brown dwarf spectral sequence and fill in the large gap in the overall spectral sequence from the hottest main-sequence stars to the coolest methane dwarfs currently known.

Single daily dose and simplified dosing regimens as a method to improve antibiotic therapy

Pharmacists can be an important member of the patient care team by assisting with the development of dosing regimens. By optimizing the pharmacokinetic properties of the antimicrobial agents, regimens can be developed that are simple to manage. Newer approaches to simplifying dosing regimens include once-daily aminoglycoside therapy, continuous infusion beta-lactams, and utilizing agents with long half-lives such as ceftriaxone and azithromycin. These efforts could result in improved compliance and in some instances decrease costs and toxicities associated with antibiotic therapy.

Extreme mortality in nineteenth-century Africa: the case of Liberian immigrants

Several studies have examined the mortality of immigrants from Europe to Africa in the nineteenth century. This paper examines the level of mortality in Liberia of Africans who emigrated there from the United States. A life table is estimated from data collected by the American Colonization Society from 1820 to 1843. The analysis reflects the mortality experience of a population that is transplanted from one disease environment to another, more exacting, disease environment. The results of this analysis show that these Liberian immigrants experienced the highest mortality rates in accurately recorded human history.

Stability of heroin hydrochloride in infusion devices and containers for intravenous administration

The stability of heroin hydrochloride in various drug-administration devices was studied. Heroin hydrochloride was supplied as the bulk powder by the National Institute on Drug Abuse and in the formulated dosage form by Evans Medical, Ltd. Stability was determined at concentrations of 1 and 20 mg/mL at room temperature (23-25 degrees C) and at 4 degrees C in a polyvinyl chloride (PVC) bag, a disposable glass syringe, and two disposable infusion devices. Studies at both concentrations also were conducted at 31 degrees C in the disposable infusion devices. All experiments were conducted in triplicate. A validated, stability-indicating, high-performance liquid chromatography assay was used. Heroin hydrochloride remained stable for a minimum of 15 days in the PVC bag and the Infusor infusion device at the tested temperatures and concentrations. In the glass syringe, heroin hydrochloride was shown to be stable for a minimum of 15 days at both 1 mg/mL and 20 mg/mL if refrigerated at 4 degrees C, whereas at room temperature it was stable for a minimum of 7 days at 1 mg/mL and for 12 days at 20 mg/mL. In the Intermate 200 infusion device, heroin hydrochloride was stable for a minimum of 15 days at both concentrations and all temperatures except for the 1 mg/mL concentration at 31 degrees C. In the latter case, stability was for a minimum of two days. No substantial changes in physical appearance or pH were observed in any of the containers under the conditions studied. Heroin hydrochloride can be repackaged in the disposable glass syringe, PVC bag, and each of the disposable infusion devices for routine clinical use.

Stability of morphine sulfate in infusion devices and containers for intravenous administration

The stability of morphine sulfate in one brand of polyvinyl chloride (PVC) container, one brand of glass syringe, and two brands of disposable infusion devices was determined. Solutions of morphine sulfate 2 and 15 mg/mL were used to fill the PVC containers and drug administration devices. Stability was determined for both concentrations of morphine sulfate at room temperature (23-25 degrees C) and 4 degrees C in the PVC containers, glass syringes, and disposable infusion devices; stability was also determined at 31 degrees C in the disposable infusion devices. At 0, 1, 2, 4, 7, 12, and 15 days, portions of the solutions were removed and assayed in triplicate by a stability-indicating high-performance liquid chromatographic method. At each time point the drug-infusion fluid combinations were inspected visually for color changes and the presence of particulate matter, and pH was measured. Morphine sulfate 2 and 15 mg/mL remained stable for at least 12 days in all the containers and devices at each temperature tested. No substantial changes in the pH or physical appearance of the solutions were observed. Morphine sulfate can be repackaged in the disposable glass syringe, PVC container, and both disposable infusion devices for routine clinical use.

Perceptions and attitudes toward nursing impairment

Perceptions and attitudes toward nursing impairment held by 1,047 registered nurses were examined. Factor analysis of the 32 Likert-type items in an original survey questionnaire revealed an underlying structure of nine dimensions characterizing attitudes toward impairment. Analyses of variance and covariance gave evidence that supervisors were more likely than staff nurses to perceive a need for disciplinary action in responding to cases of nursing impairment; staff nurses were more likely to view impairment as treatable. Significant differences were found among attitudes toward drug abuse, alcohol abuse, and emotional distress as forms of impairment.

Hearing preservation after acoustic neuroma surgery with intraoperative direct eighth cranial nerve monitoring: Part II. A classification of results

Since the advent of brainstem auditory evoked response audiometry and computerized tomography, small acoustic neuromas are more frequently found. Often the patient has serviceable hearing, which we would like to preserve during complete tumor removal. Since 1978, sixteen patients with acoustic neuromas have been operated upon through the retrosigmoid suboccipital approach, with the goal of hearing preservation. In 1983, we began using intraoperative direct eighth nerve monitoring, which produced a rapid assessment of cochlear nerve function during the excision of small acoustic neuromas. The tumors varied in size from intracanalicular lesions to one lesion with a 3.0 cm protrusion medial to the porus acousticus. In eight of sixteen cases, intraoperative monitoring was used, and in four of the patients hearing was preserved. In eight cases, intraoperative monitoring was not used, and hearing was preserved in only two patients. The overall success rate--in total tumor removal with hearing preservation--was 37%. Hearing was preserved in six of eight patients who had tumors which measured less than 1.5 cm. In this group of cases, two of the patients had a Class I good hearing result (PTA 0 to 30 dB and 70 to 100% discrimination), one patient had Class III nonserviceable hearing, (PTA 65 to 75 dB and 25 to 45% discrimination), and three patients had Class IV poor hearing, (PTA 80 to 100 dB and 0 to 20% discrimination). We found that continuous monitoring of direct eighth-nerve-evoked action potentials were extremely valuable and rapidly indicated reversible cochlear nerve trauma.

Retrolabyrinthine vestibular neurectomy with simultaneous monitoring of eighth nerve and brain stem auditory evoked potentials

We have used retrolabyrinthine vestibular neurectomy in 36 of 49 cases as the primary surgical procedure to relieve vertigo. Most of the patients (46 of 49) had Meniere's disease. Results indicate that 71% (35 of 49) of the patients had no vertigo after the operation, while 22% (11 of 49) had much improvement. Hearing was maintained within 20 dB of the preoperative level in 78% (38 of 49) of the patients. During surgery in the last 23 patients, direct nerve potentials were recorded from the middle ear promontory and the intracranial cochlear nerve. Brain stem auditory evoked responses were simultaneously recorded in the last 10 patients. It appears that the intraoperative direct cochlear nerve potentials can be used as a sensitive monitor of trauma to the cochlear nerve during and after vestibular neurectomy. If the latency of the eighth nerve action potential changes less than 0.3 msec and the waveform does not change after vestibular neurectomy, there is an excellent chance that hearing at 1 month after surgery will be within 15 dB of the level before surgery. The retrolabyrinthine vestibular neurectomy has replaced the middle fossa vestibular neurectomy and the endolymphatic subarachnoid shunt procedure in our clinic.

Conservative management of acoustic neuroma in the elderly patient

A subtotal resection through the translabyrinthine approach should be used in the treatment of large symptomatic acoustic neuromas in patients over the age of 65. This approach will consistently relieve the patient's symptoms of brain stem compression, reduce postoperative morbidity and complications, and preserve facial nerve function. In the elderly, after subtotal resection, the remaining tumor in 80% of cases appears to remain dormant during the average six year follow-up (1-16 year range). Eighty percent of acoustic neuromas not operated upon, appear to grow at a slow rate (0.2 cm/yr) while 20% grow at a fast rate (1 cm/yr). Patients over the age of 65 with small acoustic neuromas do not need surgical intervention. Yearly CT scanning is recommended to determine the growth rate of the acoustic neuroma. A conservative approach should be used in the treatment of all acoustic neuromas in the elderly.