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Biomedical subjects

J A Howell

Publications and source records attributed to J A Howell.

At least 19 recordsLinked to original sources
PubMed2003

Membrane bioreactors for treating waste streams.

Membrane bioreactors (MBRs) have a number of advantages for treating wastewater containing large quantities of BOD. This paper reviews the inherent advantages of an MBR, which include high potential biomass loadings, lower sludge yields, and retention of specialized organisms that may not settle well in clarifiers. A major problem in effluent treatment occurs when mixed inorganic and organic wastes occur with high concentrations of pollutants. Inorganics that might cause extremes of pH and/or salinity will inhibit microbial growth and only specialized organisms can survive under these conditions. Refractory organics are only biodegraded with difficulty by specialized organisms, which usually do not resist the extreme inorganic environments. The use of membrane bioreactors to help separate the micro-organisms from the inorganic compounds, yet permit the organics to permeate, has been developed in two different designs that are outlined in this paper. The use of membrane contactors in a multimembrane stripping system to treat acidic chlorinated wastes is proposed and discussed.

Biomass↗
PubMed2003

Turnup turndown of membrane operation of membrane bioreactors.

Membrane bioreactors can be operated with intermittent permeation and continuous aeration. Aeration close to the surface of a submerged membrane helps to maintain a membrane surface that is free from fouling. The conditions under which this occurs depend on the interaction between flux and aeration rate. Increased flux is possible without severe fouling if the aeration rate is increased. Results of performing membrane operation under the dual intermittency of aeration rate and permeation rate, with permeation also interrupted on a regular cycle, are presented. The results show that membrane plants designed for optimal operation at moderate flux can survive effectively with higher flux operation for restricted periods. Designing to account for such effects could reduce overall plant costs.

Chemistry Techniques, Analytical↗
PubMed2003

Content of ileal EAAC1 and hepatic GLT-1 high-affinity glutamate transporters is increased in growing vs. nongrowing lambs, paralleling increased tissue D- and L-glutamate, plasma glutamine, and alanine concentrations.

Glutamate is a central metabolite for whole-animal energy and N metabolism. This study tested the hypothesis that ileal epithelium, liver, and kidney content of system X-(AG) glutamate transporters EAAC1 and GLT-1 would be up-regulated to support growth of wethers (30 +/- 1.2 kg) fed a forage-based diet for at least 14 d to gain (2.0 x NEm; n = 9) vs. maintain (1.2 x NEm; n = 9) BW. We have previously demonstrated that two high-affinity glutamate transporters (EAAC1, GLT-1) are expressed by these extensive glutamate metabolizing epithelial tissues. Wethers fed at 2.0 x NEm gained (P < 0.001; 0.26 kg/d) BW, whereas those fed 1.2 x NEm did not. Although plasma concentrations (microM) of glucose and L- or D-glutamate did not differ, plasma glutamine (precursor of glutamate) and alanine concentrations (transamination product of glutamate) were 28% (P < 0.007) and 22% (P < 0.072) greater for growing lambs than nongrowing lambs. In tissues, the concentration of L-glutamate in ileum epithelia and D-glutamate of liver was 49% (P < 0.015) and 181% (P < 0.042) greater, respectively, in growing vs. nongrowing animals, whereas concentrations of glutamate isoforms did not differ in kidney. Paralleling these increased amino acid concentrations, ileal epithelium contained 313% more (P < 0.038) EAAC1 protein and liver contained 240% more (P < 0.001) GLT-1 protein, whereas kidney transporter content did not differ between growing and nongrowing wethers. In contrast to increased EAAC1 and GLT-1 protein content in ileal and liver tissue of growing lambs, messenger RNA levels did not differ. These results indicate that the increased capacity for high-affinity glutamate uptake in growing vs. nongrowing lambs is achieved through increased expression of EAAC1 by ileal epithelium and GLT1 by liver, which parallel increased tissue concentrations of glutamate and plasma concentrations of two major interorgan N carriers, glutamine and alanine.

Alanine↗
PubMed2002

Use of porcine zona pellucida (PZP) vaccine as a contraceptive agent in free-ranging tule elk (Cervus elaphus nannodes).

The potential for the application of porcine zona pellucida (PZP) immunocontraception in wildlife population management has been tested over a 15 year period and promises to provide a useful wildlife management tool. These studies have provided evidence indicating that the use of PZP immunocontraception in wildlife: (i) is effective at both the physiological and population level (Liu et al., 1989; Kirkpatrick et al., 1996; Turner et al., this supplement); (ii) is deliverable by remote means (Kirkpatrick et al., 1990; Shideler, 2000); (iii) is safe in pregnant animals (Kirkpatrick and Turner, this supplement); (iv) is reversible (Kirkpatrick et al., 1991; Kirkpatrick and Turner, this supplement); (v) results in no long-term debilitating health problems (Kirkpatrick et al., 1995; Turner and Kirkpatrick, this supplement); (vi) has no implications for passage through the food chain (Harlow and Lane, 1988); and (vii) is reasonably inexpensive (J. F. Kirkpatrick, personal communication). This report presents the results of a 5 year study in tule elk (Cervus elaphus nannodes), 3 years of which were on the application of PZP immunocontraception to an expanding elk population living in a wilderness area of Point Reyes National Seashore in Marin County, CA, where hunting is not allowed and culling is not publicly acceptable.

Animals↗
PubMed2001

Molecular identification of high-affinity glutamate transporters in sheep and cattle forestomach, intestine, liver, kidney, and pancreas.

Glutamate metabolism is essential to support many facets of metabolism. The objective of this study was to determine the tissue distribution of glutamate transporters known to support the tissue metabolism of glutamate. The expression of proteins capable of high-affinity glutamate transport (system X-(AG)) by epithelia isolated from the rumen, omasum, duodenum, jejunum, ileum, cecum, and colon and homogenates of liver, kidney, and pancreatic tissues from wethers (n = 4; BW = 28.4 +/- 8.4 kg) and steers (n = 3; BW = 426 +/- 32.3 kg) fed forage-based diets was evaluated by immunoblot analysis. Proteins EAAC1 (62, 93 kDa) and GLT-1 (142, 188, >202 kDa) were expressed by every tissue examined. In contrast, GLAST1 (140 kDa) was expressed only by the pancreas, and EAAT4 (67 kDa) was detected only in sheep brain. To corroborate protein expression data, the presence and size of transporter mRNA in ileal, liver, and pancreatic homogenates were evaluated by Northern analysis. GLAST1 mRNA (2.4, 4.3 kb) was detected only in the pancreas, whereas EAAC1 (2.2, 2.8 kb) and GLT-1 (12.1 kb) mRNA transcripts were detected in all three tissues. The expression of EAAT4 and GLT-1 mRNA was confirmed by reverse transcriptase-polymerase chain reaction analyses. Sequencing of the resulting partial-length ovine GLT-1 cDNA revealed 100% identity with the rat homolog. Overall, these data demonstrate that sheep and cattle share the same pattern of system X-(AG) transporter expression, which differed among tissues and transporter isoforms. Accordingly, these data provide the fundamental knowledge to initiate research that determines whether the expression of high-affinity glutamate transporters by ruminants is sensitive to ontogenic and(or) dietary regulation.

ATP-Binding Cassette Transporters↗
PubMed2000

Insulin-like growth factor II supply modifies growth of intestinal adenoma in Apc(Min/+) mice.

Insulin-like growth factor-II (IGF-II) is an embryonic growth promoter and cell survival factor. IGF-II supply is normally limited by gene expression because transcription occurs predominantly from the paternal allele in mouse and man (maternal imprinting). Excess IGF-II has detrimental systemic and local effects in vivo, promoting somatic overgrowth and an increased frequency of tumors. IGF2 mRNA is overexpressed in colorectal and many other human cancers. In this paper, we show that altered IGF-II supply modifies intestinal tumor growth. Mice genetically altered in the IGF-II system were combined in crosses with ApcMin/+, a murine model of human familial adenomatous polyposis. Depending on genetic background, ApcMin/+ acquires multiple small intestinal adenoma before becoming moribund with anemia. Mice that express excess IGF-II delivered using a bovine keratin 10 promoter (k10Igf2/+) develop a disproportionate overgrowth of colon, uterus, and skin. Combination with ApcMin/+ leads to a 10-fold increase in the number and the diameter of colon adenoma (P<0.0001) compared to ApcMin/+ littermate controls (postnatal day 80), an increased susceptibility to rectal prolapse (41%), and a histological progression to carcinoma. Mice with reduced IGF-II supply, secondary to the disruption of the paternal Igf2 allele (Igf2+m/-p), are 60% the weight of wild-type littermates. Combination with ApcMin/+ leads to a 3-fold reduction in small intestinal adenoma number (P<0.0001) compared to ApcMin/+ littermate controls (postnatal day 150), and a significant decrease in adenoma diameter (P<0.001). With in situ hybridization, we show that Igf2 was expressed in all adenoma irrespective of IGF-II supply. This suggests that there is an increased maternal allele expression of Igf2 (loss of imprinting) in adenoma which form, despite paternal Igf2 allele disruption. We conclude that IGF-II supply is a modifier of intestinal adenoma growth, and we provide genetic evidence for its functional role in colorectal cancer progression.

Adenoma↗
PubMed2000

Dietary carbohydrate source and energy intake influence the expression of pancreatic alpha-amylase in lambs.

In ruminants, pancreatic alpha-amylase is the primary enzyme responsible for the initial hydrolysis of alpha-linked glucose in the small intestinal lumen. The objective of this experiment was to examine the effects of altered dietary starch and energy supply on the expression of pancreatic alpha-amylase mRNA, protein and activity in lambs. Wether lambs (n = 24; 28 +/- 0.5 kg body weight) were fed low or high starch diets at 1.2 or 1.8 x net energy of maintenance for at least 28 d before tissue collection. Lambs fed the high energy/high starch diet tended to have more pancreatic alpha-amylase protein (54.5 kDa; P: = 0.08) and had greater activity (P: = 0.03), but alpha-amylase mRNA (1.6 kb) tended to be lower (P: = 0.17). Additionally, rumen fluid total short-chain fatty acid concentration was greater (P: = 0.04) and plasma glucose concentration tended to be greater (P: = 0.07) in lambs fed the high energy/high starch diet. However, pancreatic trypsinogen protein (25. 5 kDa) and jejunal maltase activity were not influenced by dietary treatment, suggesting that different regulatory systems are involved in regulating the tissue protein or activity levels of these two enzymes compared with alpha-amylase. These data suggest that dietary regulation of pancreatic alpha-amylase expression in ruminants is complex and probably regulated by transcriptional and post-transcriptional events.

Animals↗
PubMed1998

Improved protein refolding using hollow-fibre membrane dialysis.

We have used a cellulose acetate, hollow-fibre (HF) ultrafiltration membrane to refold bovine carbonic anhydrase, loaded into the lumen space, by removing the denaturant through controlled dialysis via the shell side space. When challenged with GdnHCl-denatured carbonic anhydrase, 70% of the loaded protein reptated through the membrane into the circulating dialysis buffer. Reptation occurred because the protein, in its fully unfolded configuration, was able to pass through the pores. The loss of carbonic anhydrase through the membrane was controlled by the dialysis conditions. Dialysis against 0.05 M Tris-HCl for 30 min reduced the denaturant around the protein to a concentration that allowed the return of secondary structure, increasing the hydrodynamic radius, thus preventing protein transmission. Under these conditions a maximum of 42% of carbonic anhydrase was recovered (from a starting concentration of 5 mg/mL) with 94% activity. This is an improvement over refolding carbonic anhydrase by simple batch dilution, which gave a maximum reactivation of 85% with 35% soluble protein yield. The batch refolding of carbonic anhydrase is very sensitive to temperature; however, during HF refolding between 0 and 25 degrees C the temperature sensitivity was considerably reduced. In order to reduce the convection forces that give rise to aggregation and promote refolding the dialyzate was slowly heated from 4 to 25 degrees C. This slow, temperature-controlled refolding gave an improved soluble protein recovery of 55% with a reactivation yield of 90%. The effect of a number of additives on the refolding system performance were tested: the presence of PEG improved both the protein recovery and the recovered activity from the membrane, while the detergents Tween 20 and IGEPAL CA-630 increased only the refolding yield.

Animals↗
PubMed1994

Operational properties of an inverted matrix cellulose CM ion-exchanger.

Productive CM is a recently available carboxymethyl ion-exchanger based on cellulose supplied by BPS Separation. It is supplied in an 'inverted matrix' form as a coherent structure with large voids and about 90% free volume. This paper reports mainly on the physical properties and robustness under normal use conditions using lysozyme as a model protein. The structure is shown by electron microscopy to be formed of fibrous or sheet material around macropores of around 100 microns in diameter. The material around the macropores is itself porous down to the smallest pores visible at perhaps 50 nm. The capacity under static and dynamic conditions was measured and found in both cases to be only slightly dependent on applied flow velocities up to 8 m h-1. The high porosity allowed cider fermentation broth and diluted egg white to be applied directly to a column without blockage and at a moderate pressure drop yet with a high superficial velocity. Compression of the bed at high flow rates did not occur at free space velocities up to 17 m h-1 with water and slightly lower with other fluids. The adsorption isotherm was determined and found to follow a Langmuir form. It proved to be totally stable to immersion in 1 M NaOH and 1 M NaCl without any measurable volume changes. Many of the properties were compared with those of other ion-exchange resins and found to be equivalent in capacity but superior in terms of stability, sustainable flow rates and dynamic capacity. It is concluded that the stability, performance under high flow rates and good capacity make it eminently suitable for use in large scale applications.

Adsorption↗
PubMed1991

Resolution and productivity of conalbumin and lysozyme from fresh egg-white loaded at very high flow rate on a 250-mm length CM-HVFM column.

A 250 x 10 mm I.D. column of CM-HVFM, a novel carboxymethyl ion-exchange matrix, has been used as a preparative chromatographic column to separate fresh egg-white protein. When loading a diluted egg-white solution at pH 4.8 ovalbumin was not adsorbed and lysozyme was preferentially adsorbed compared to the conalbumin. As the column loading was increased from 24 to 450 kg m-3 column volume at the superficial velocity of 6.12 m h-1, the lysozyme continued to be absorbed eventually displacing conalbumin. A maximum lysozyme productivity at 16.7 kg m-3 h-1 was achieved at the highest loading. For conalbumin a maximum productivity of 8.8 kg m-3 h-1 occurred at the lower loading of 100 kg m-3. The purities of lysozyme and conalbumin were comparable at a column loading of 450 kg m-3 h-1. The performance of the column was not degraded, neither was the column blocked or channelled despite the high column loading at the high flow-rate.

Animals↗
PubMed1987

High performance liquid chromatographic determination of thromboxane B2 in human serum as a methoxime-panacylester derivative.

A high performance liquid chromatographic (HPLC) method was developed to measure thromboxane B2 (TxB2) levels in human serum. Serum samples (2 mL) were extracted using solid phase extraction columns in a C 18/silica mode sequencing approach. The internal standard, 6-ketoprostaglandin F1 alpha, was added to the serum extracts. The eicosanoids were doubly derivatized, first with panacyl bromide, then with methoxyamine to form methoxime-panacyl ester derivatives. The eicosanoid derivatives were chromatographed using a reverse phase HPLC system with UV detection (254 nm). Assay linearity was demonstrated with fortified TxB2 standards in 3% bovine serum albumin over a range of 25 to 500 ng/mL (r greater than or equal to 0.994). There was no significant interday difference or bias in assay results for pooled standards at 75, 226 and 376 ng/mL concentrations (p greater than 0.05). Pooled estimates of precision at these levels indicate an assay relative standard deviation 6-9%. The HPLC assay was used to quantitate TxB2 levels in human serum. Results were consistent with previously published values when drug-free serum was analyzed to assess ex vivo TxB2 formation.

6-Ketoprostaglandin F1 alpha↗
PubMed1985

Post-column reaction detection system for the determination of organophosphorus compounds by liquid chromatography.

The development and application of a post-column reaction detection system for organophosphorus compounds based upon their photodegradation to ortho-phosphate followed by the formation of reduced heteropolymolybdate is reported. Photodegradation occurs in a fused-silica tube coiled about a 450-W xenon lamp in the presence of ammonium peroxydisulfate. Photodegradation yields were practically quantitative for the organophosphates, -phosphonates, and -phosphorodithioates tested. Factors affecting the rate of the chromogenic reaction were optimized so that its contribution to the total band-broadening was negligible. The effect of interfering organic modifiers in the mobile phase was studied using the acetate ion as a model. Separations were developed using no organic solvents in the mobile phases. The determination of dialkylphosphates in urine and organophosphorus pesticides in tomatoes illustrate the potential of the methodology.

Animals↗
PubMed1972

A scanning x-ray microscope using synchrotron radiation.

Focused synchrotron radiation collimated by means of a pinhole has been used to construct a scanning x-ray microscope capable of making stereoscopic element-discriminating pictures of relatively thick specimens in an atmospheric environment.

Microscopy, Electron, Scanning↗