Biomedical subjects

S M Potter

Publications and source records attributed to S M Potter.

32 records · Page 2Linked to original sources

PubMed1996

Soy protein concentrate and isolated soy protein similarly lower blood serum cholesterol but differently affect thyroid hormones in hamsters.

There is a wide variation in the hypocholesterolemic response to ingestion of soy protein in humans. One possible explanation is that the different soy protein preparations used contain different spectra of biologically active components. This could affect a number of indices including thyroid hormone status. An increased level of thyroxine has been proposed as an underlying mechanism of the hypocholesterolemic effect of soy protein. The objective of this study was to determine if serum cholesterol and thyroid hormone concentrations differed because of feeding soy protein from different sources. Twenty-nine male weanling golden Syrian hamsters were fed rations containing 25 g/100 g protein from either isolated soy protein (ISP), soy protein concentrate (SPC) or casein for 35 d. Serum total cholesterol concentrations were lower in hamsters fed ISP and SPC compared with those fed casein (P < 0.05). No differences in cholesterol concentrations were observed in lipoprotein fractions. Serum thyroxine and free thyroxine were greater only in hamsters fed ISP than in those fed casein (P < 0.05), whereas triiodothyronine concentrations were higher in casein-fed than in SPC-fed hamsters (P < 0.05). Results indicate that protein from ISP and SPC are both effective in lowering blood cholesterol concentrations, whereas only ISP increases thyroxine concentrations. Therefore, it appears unlikely that modulation of thyroid hormone status is responsible for the cholesterol-lowering effect of soy protein.

Animals↗

PubMed1996

Soy protein and serum lipids.

Evidence exists indicating that substitution of soy for animal protein reduces both total ahd LDL-cholesterol concentrations in humans. There are a number of biologically active compounds associated with soy protein; however, the precise mechanism and the component(s) of soy responsible have not been fully established. Some studies suggest that, when soy protein is fed, cholesterol absorption or bile acid reabsorption, or both, is impaired. This is observed in some animal species such as rabbits and rats but not in humans, nor when amino acids replace intact soy protein. Other workers have proposed that changes in endocrine status are responsible, however, this again has not been observed in humans. Increases in LDL receptor activity in both animals and humans have been reported after ingestion of soy protein or various extracts of soy, or both. Furthermore, the soybean isoflavone genistein may inhibit lesion and thrombus formation via inhibition of second messengers.

Animals↗

PubMed1996

Neural transplant staining with DiI and vital imaging by 2-photon laser-scanning microscopy.

We are developing a multielectrode silicon "neuroprobe" for maintaining a long-term, specific, two-way electrical interface with nervous tissue. Our approach involves trapping a neuron (from an embryonic rat hippocampus) in a small well with a stimulation/recording electrode at its base. The well is covered with a grillwork through which the neuron's processes are allowed to grow, making synaptic contact with the host tissue, in our case a cultured slice from a rat hippocampus. Each neuroprobe can accommodate 15 neurons, one per well. As a first step in studying neurite outgrowth from the neuroprobe, it was necessary to develop new staining techniques so that neurites from the probe neurons can be distinguished from those belonging to the host, without interference from non-specific background staining. We virtually eliminated background staining through a number of innovations involving dye solubility, cell washing, and debris removal. We also reduced photobleaching and phototoxicity, and enhanced imaging depth by using a 2-photon laser-scanning microscope. We focused on using the popular membrane dye, DiI, however a number of other membrane dyes were shown to provide clear images of neural processes using pulsed illumination at 900 nm. These techniques will be useful to others wishing to follow over time the growth of neurons in culture of after transplantation in vivo, in a non-destructive way.

Animals↗

PubMed1995

Overview of proposed mechanisms for the hypocholesterolemic effect of soy.

A large body of literature indicates that protein from soybeans reduces blood cholesterol concentrations in experimental animals as well as in humans. The mechanism and component of soy responsible has not been established fully. Some suggest that when soy protein is fed, cholesterol absorption and/or bile acid reabsorption is impaired. This is observed in some animal species, such as rabbits and rats, but not in humans nor when amino acids replace intact soy protein. Others propose that changes in endocrine status, such as alteration in insulin:glucagon ratio and thyroid hormone concentrations, are responsible. The metabolic changes that have been observed on soy protein feeding in a variety of animal models, and in some cases humans, include increased cholesterol synthesis, increased bile acid synthesis (or fecal bile acid excretion), increased apolipoprotein B or E receptor activity and decreased hepatic lipoprotein secretion and cholesterol content, which are associated with an increased clearance of cholesterol from the blood. One hypothesis suggests amino acid composition or proportionality of soy causes changes in cholesterol metabolism (possibly via the endocrine system). Others have proposed that nonprotein components (such as saponins, fiber, phytic acid, minerals and the isoflavones) associated with soy protein affect cholesterol metabolism either directly or indirectly.

Animals↗

PubMed1994

Intake of 25 g of soybean protein with or without soybean fiber alters plasma lipids in men with elevated cholesterol concentrations.

Twenty-one mildly hypercholesterolemic men consumed a diet that was low in fat (< 30% of energy) and cholesterol (300 mg/d) and were given muffins containing 25 g protein + 20 g dietary fiber daily from either isolated soybean protein + soybean cotyledon fiber, isolated soybean protein + cellulose, casein + soybean cotyledon fiber or casein + cellulose. All subjects progressed through the low fat, low cholesterol baseline period, lasting 2 wk, and then through all four dietary treatments, lasting 4 wk each, according to a Latin square design. Plasma concentrations of total, LDL, HDL and VLDL cholesterol, total and VLDL triacylglycerols, and apolipoprotein A-I and B were measured at the end of each period. When data from all subjects were analyzed, dietary treatments did not influence lipemia; however, in subjects with initial total cholesterol concentrations > 5.7 mmol/L, both isolated soybean protein treatments resulted in significantly lower total cholesterol compared with the two casein treatments (P < 0.05). In addition, a negative linear relationship was observed when a subject's total or LDL cholesterol change after each of the soybean treatments was regressed against the subject's baseline cholesterol concentration (P < 0.05). Apolipoprotein A-I varied dependent on baseline cholesterol with no apparent pattern, whereas apolipoprotein B levels were not affected. Results indicate that consumption of 25 g soybean protein/d is associated with lower total cholesterol concentrations in individuals with initial cholesterol concentrations > 5.7 mmol/L.

Adult↗

PubMed1994

Mongolian gerbils (Meriones unguiculatus) absorb beta-carotene intact from a test meal.

Because a yellow color has been observed in the fat pads of Mongolian gerbils fed a nonpurified diet, we designed the current study to determine whether adult male gerbils would absorb beta-carotene intact from a test meal. Thirty-five gerbils (80-90 g) were adapted to the laboratory and fed a standard purified diet free of beta-carotene for 16-19 d. Gerbils were then fed a test meal consisting of 279 nmol of beta-carotene as 10% water-soluble beadlets suspended in 0.5 mL of Ensure. Gerbils (n = 5) were killed at 0, 2, 4, 6, 12, 24 or 72 h after the test meal, blood was obtained by cardiac puncture, and tissues were taken for beta-carotene analysis. No beta-carotene was detected in serum at 0 or 72 h, whereas beta-carotene was present at all other sampling times. Serum beta-carotene peaked at 4 h, at a level of 88 nmol/L. beta-Carotene was detected in the liver of all groups; however, the concentration increased from -34 pmol/g to a maximum concentration of 926 pmol/g at 24 h after the test meal. Other tissues also contained beta-carotene. The results demonstrate that Mongolian gerbils, like ferrets and preruminant calves, absorb beta-carotene intact when beta-carotene is provided at a physiological level in a test meal. This species may be particularly useful for evaluation of the role of antioxidants, such as beta-carotene, in LDL oxidation.

Administration, Oral↗

PubMed1993

In vitro aging of calmodulin generates isoaspartate at multiple Asn-Gly and Asp-Gly sites in calcium-binding domains II, III, and IV.

We have determined the major sites responsible for isoaspartate formation during in vitro aging of bovine brain calmodulin under mild conditions. Protein L-isoaspartyl methyltransferase (EC 2.1.1.77) was used to quantify isoaspartate by the transfer of methyl-3H from S-adenosyl-L-[methyl-3H]methionine to the isoaspartyl (alpha-carboxyl) side chain. More than 1.2 mol of methyl-acceptor sites per mol of calmodulin accumulated during a 2-week incubation without calcium at pH 7.4, 37 degrees C. Analysis of proteolytic peptides of aged calmodulin revealed that > 95% of the methylation capacity is restricted to residues in the four calcium-binding domains, which are predicted to be highly flexible in the absence of calcium. We estimate that domains III, IV, and II accumulated 0.72, 0.60, and 0.13 mol of isoaspartate per mol of calmodulin, respectively. The Asn-97-Gly-98 sequence (domain III) is the greatest contributor to isoaspartate formation. Other major sites of isoaspartate formation are Asp-131-Gly-132 and Asp-133-Gly-134 in domain IV, and Asn-60-Gly-61 in domain II. Significant isoaspartate formation was also localized to Asp-20, Asp-22, and/or Asp-24 in domain I, to Asp-56 and/or Asp-58 in domain II, and to Asp-93 and/or Asp-95 in domain III. All of these residues are calcium ligands in the highly conserved EF-hand calcium-binding motif. Thus, other EF-hand proteins may also be subject to isoaspartate formation at these ligands. The results support the idea that isoaspartate formation in structured proteins is strongly influenced by both the C-flanking residue and by local flexibility.

Amino Acid Sequence↗

PubMed1993

Depression of plasma cholesterol in men by consumption of baked products containing soy protein.

The effects of soy-protein consumption with and without soy fiber on plasma lipids in 26 mildly hypercholesterolemic men were studied. Four, 4-wk dietary treatments included 50 g protein and 20 g dietary fiber from soy flour (SF), isolated soy protein/soy cotyledon fiber (ISP/SCF), ISP/cellulose (ISP/C), or nonfat dry milk/C (NFDM/C) in conjunction with a low-fat, low-cholesterol diet. Plasma total cholesterol (TC) concentrations were lowest for both ISP dietary treatments compared with baseline (P < 0.05) and NFDM/C (P < 0.01). SF also led to lower TC compared with NFDM/C (P < 0.05). LDL-cholesterol values were lowest for both ISP treatments compared with NFDM/C (P < 0.01), but lower compared with baseline only with ISP/SCF (P < 0.05). Apolipoprotein B was lowest when ISP/C was fed, compared with baseline, SF, and NFDM (P < 0.05). HDL-cholesterol and total triglycerides (TG) were not affected. Results indicate that 50 g ISP is effective in lowering TC, LDL-C, and apolipoprotein B while maintaining HDL concentrations in mildly hypercholesterolemic men.

Adult↗

PubMed1992

The type II isoform of bovine brain protein L-isoaspartyl methyltransferase has an endoplasmic reticulum retention signal (...RDEL) at its C-terminus.

Bovine brain is known to contain two major isoforms of protein L-isoaspartyl methyltransferase (PIMT), an enzyme that facilitates repair of atypical L-isoaspartyl peptide bonds in proteins. Although the two isoforms can be separated by anion-exchange chromatography, they appear to have similar, if not identical, substrate specificities in vitro. The more basic type I isoform has been extensively characterized, and its complete sequence has been reported. The present study was undertaken in an attempt to understand the structural and functional uniqueness of the more acidic type II isoform. Electrospray mass spectrometry of the intact enzymes revealed that the type II isoform is approximately 43 amu heavier than the type I isoform. Cyanogen bromide cleavage followed by HPLC with on-line mass analysis revealed that the type II isoform contains a unique C-terminal fragment which is 43 amu heavier than the corresponding fragment from the type I isoform. Amino acid composition analysis and direct sequencing of this fragment indicate that the type II isoform ends in the sequence ...RDEL, while the type I is known to end in ...RWK. Since ...RDEL, like ...KDEL, serves as an effective endoplasmic reticulum retention signal, we propose that the type II isoform serves to repair damaged proteins within the endoplasmic reticulum or, perhaps, within some other specialized compartment of the cell. Comparison of the protein sequences of the two bovine brain isoforms to DNA sequences for rodent PIMT reported by others suggests that the type II isoform may be produced by splicing within the codon for Arg224.

Amino Acid Sequence↗

PubMed1990

Influence of sulfur-amino acid content variation in plant vs animal protein on serum and tissue lipids in rats.

The objective of the study was to determine the effects of methionine and cysteine supplementation of soy protein isolate and casein on serum and tissue lipid levels in rats. Sixty male, weanling, Wistar-Kyoto rats were fed two sources of protein (casein or soy protein isolate) and three variations of sulfur-amino acid supplementation (none, methionine, or cysteine). At this level of protein intake (10% by weight), rats fed soy-based diets had similar serum lipid concentrations than rats fed casein-based diets. Choline was not added to the diet in order to be able to assess independent influences of methionine and cysteine on lipid metabolism. Overall, serum lipid values were greater in rats fed proteins supplemented with methionine while the addition of cysteine produced lower lipid levels. Liver lipid concentrations were increased tremendously upon cysteine supplementation of soy protein isolate. Protein quality, as determined by protein efficiency ratio, was improved by supplementation of either sulfur-amino acid; however, methionine had the greatest effect. Results indicate that the sulfur-amino acids influence lipid metabolism in the absence of dietary choline. The mechanism by which this occurs is not known.

Animals↗

PubMed1990

Dietary protein source and plasma lipid profiles of infants.

Total cholesterol and triglyceride concentrations were measured in plasma samples taken at 4 and 8 weeks of age from 40 full-term infants who had been fed either human milk or one of three formulas containing casein-to-whey ratios of 82:18, 66:34, or 50:50 to investigate whether dietary protein influenced the development of plasma lipid profiles. Infants fed the formula with the casein-to-whey ratio of 82:18 had significantly higher plasma cholesterol levels at both 4 and 8 weeks of age compared with other groups of infants (P less than .05). Infants fed the high-casein formula also showed an increase in plasma cholesterol levels with time (P less than .001). Plasma triglyceride concentrations decreased as concentration of casein decreased (P less than .05) among the formula-fed groups and increased with time. Infants fed human milk had plasma triglyceride concentrations similar to those infants who had been fed the 82:18 formula at 4 weeks of age; however, triglyceride concentrations eventually fell and were similar to those concentrations in infants who had been fed the 50:50 formula at 8 weeks of age. Results indicate that constituent lipids of human milk or formulas were not determining factors for changes observed in plasma cholesterol levels and triglyceride concentrations among groups. Since formulas differed only in proteins and their constituent amino acids, further investigation of the impact of dietary protein (amino acids) on development of blood lipid profiles in infants is warranted.

Caseins↗

PubMed1989

Dichotic listening indices of right hemisphere semantic processing.

A new dichotic listening technique, based on a psychophysical threshold procedure and providing ordinal scale measurement of lateral asymmetry, was used to investigate variation in the size of right-ear advantage for verbal vs manual response modalities across three semantic categories of stimuli in 60 right-handed males. For manual responders, abstract words elicited a significantly greater right-ear advantage than did concrete words, while emotional words elicited a non-significant left-ear advantage. Verbal responders showed no significant difference in the size of right-ear advantage across stimuli. The results suggest that both response modality and stimulus type are important variables for dichotic listening paradigms seeking evidence of right hemisphere contributions to semantic processing.

Adult↗

PubMed1988

Is interhemispheric transfer related to handedness and gender?

Interhemispheric transfer was assessed by five motor, tactile and visual tasks which required the 48 subjects to compare stimuli presented simultaneously on both sides of the body midline. Non-right-handers performed significantly better than consistent right-handers on one motor and one tactile task. Females out-performed males on the visual task and on one tactile task. Better interhemispheric transfer performance by non-right-handers and by females may be related to the reportedly larger corpus callosum regions in these groups and also to the reportedly less strong lateralization of function.

Adult↗

PubMedDate not supplied

Protein and fat utilization by humans as affected by calcium phosphate, calcium carbonate, and manganese gluconate supplements.

The object of this study was to determine the effect of calcium carbonate or calcium phosphate supplements on dietary protein and fat utilization from low and high manganese diets. During the 63-day study, the 14 human adult subjects ate a constant laboratory controlled diet. In separate periods, subjects consumed the basal diet alone or with supplements of calcium carbonate, calcium carbonate plus manganese gluconate, calcium phosphate, or calcium phosphate plus manganese gluconate. Contrast analyses of data indicated that manganese gluconate supplementation of diets, when combined with either calcium phosphate or calcium carbonate, increased fecal losses of fat. When used as single supplements, both calcium phosphate and calcium carbonate depressed fecal fat loss in comparison with values when no supplements were used. Manganese gluconate supplements depressed fecal nitrogen losses calculated as a percentage of dry fecal weight.

Adult↗