Biomedical subjects

P L Colvin

Publications and source records attributed to P L Colvin.

11 recordsLinked to original sources

PubMed2001

Dietary n-3 polyunsaturated fat increases the fractional catabolic rate of medium-sized HDL particles in African green monkeys.

We have previously described a novel pathway for the metabolism of HDL subfractions in which small [2 apolipoprotein (apoA-I) molecules per particle] HDL particles are converted in a unidirectional manner outside the plasma compartment to medium (3 apoA-I molecules per particle) or large (4 apoA-I molecules per particle) HDL particles, which are subsequently removed from the circulation by the liver (Colvin et al. 1999. J. Lipid Res. 40: 1782;-1792; Huggins et al. 2000. J. Lipid Res. 41: 384;-394). The purpose of the present study was to determine whether the reduction in concentration of medium HDL in African green monkeys consuming n-3 polyunsaturated versus saturated fat diets resulted from decreased in vivo production or increased catabolism. Tracer small LpA-I (HDL containing only apoA-I) were isolated, without ultracentrifugation, by gel filtration and immunoaffinity chromatography and radiolabeled. After injection, the specific activity of apoA-I in small, medium, and large HDL was determined, and the kinetic data were analyzed using our previously published multicompartmental model for HDL subfraction metabolism. We found a significant reduction of apoA-I concentration in medium HDL in the animals fed n-3 polyunsaturated fat (31.2 +/- 0.7 mg/dl) compared with animals fed saturated fat (85.4 +/- 11.9 mg/dl; P = 0.002). The production rates of apoA-I in small, medium, and large HDL were similar in both diet groups; however, there was a significant increase in the fractional catabolic rate of apoA-I in medium HDL in the animals fed n-3 polyunsaturated fat (2.188 +/- 0.501 pools/day) compared with animals fed saturated fat (0.714 +/- 0.191 pools/day; P = 0.02). We conclude that n-3 polyunsaturated fat reduces HDL cholesterol concentration by increasing the fractional catabolic rate of medium-sized HDL particles in African green monkeys.

Animals↗

PubMed1999

Metabolism of high density lipoprotein subfractions.

Over the past few years, new experimental approaches have reinforced the awareness among investigators that the heterogeneity of HDL particles indicates significant differences in production and catabolism of HDL particles. Recent kinetic studies have suggested that small HDL, containing two apolipoprotein A-I molecules per particle, are converted in a unidirectional manner to medium HDL or large HDL, containing three or four apolipoprotein A-I molecules per particle, respectively. Conversion appears to occur in close physical proximity with cells and not while HDL particles circulate in plasma. The medium and large HDL are terminal particles in HDL metabolism with large HDL, and perhaps medium HDL, being catabolized primarily by the liver. These novel kinetic studies of HDL subfraction metabolism are compelling in-vivo data that are consistent with the proposed role of HDL in reverse cholesterol transport.

Animals↗

PubMed1999

Small HDL particles containing two apoA-I molecules are precursors in vivo to medium and large HDL particles containing three and four apoA-I molecules in nonhuman primates.

We hypothesized that small HDL particles, containing two apoA-I molecules but no apoA-II (LpAI), may be converted in vivo into medium and large HDL particles, containing three or four apoA-I molecules, respectively, and that more conversion will occur in animals with higher HDL concentrations. To test this possibility, kinetic studies of small LpAI were performed in African green monkeys with either high plasma HDL cholesterol concentrations (120 +/- 36 mg/dl, mean +/- SD, n = 3) or low plasma HDL cholesterol concentrations (40 +/- 13 mg/dl, n = 3). Tracer small LpAI was purified, without ultracentrifugation, by immunoaffinity and gel filtration. After injection, the specific activity of apoA-I in small, medium, and large HDL, consisting of both LpAI and LpAI:AII particles, was followed. A multicompartmental model was developed with the simultaneous analysis of urine and plasma turnover data for the kinetics of apoA-I in small, medium, and large HDL. These analyses indicated that small HDL is converted to either medium or large HDL with little or no interconversion of medium HDL and large HDL. Much of the metabolic conversion of small HDL occurs in a sequestered pool, effectively outside the circulating plasma, in a unidirectional manner before reentering the circulating plasma as medium or large HDL. The mean fractional catabolic rate of apoA-I in small, medium, and large HDL was not different comparing the high and low HDL group. In contrast, the mean production rate of apoA-I was greater in the high HDL group compared with the low HDL group. These data support the hypothesis that the plasma concentration of HDL is primarily a function of the rate of appearance of apoA-I in medium and large HDL.

Animals↗

PubMed1998

Sex steroids increase cholesterol 7alpha-hydroxylase mRNA in nonhuman primates.

One mechanism that may account for our prior observation that oral contraceptives decrease the hepatic cholesterol concentration independently of the low-density lipoprotein (LDL) receptor in sexually intact nonhuman primates is that sex hormones increase biliary cholesterol secretion by increasing hepatic mRNA abundance for cholesterol 7alpha-hydroxylase, the rate-limiting enzyme in the conversion of cholesterol into bile acids. To examine the independent effect of estrogen, progestin, and combined estrogen and progestin on the hepatic cholesterol concentration and cholesterol 7alpha-hydroxylase mRNA abundance, 34 ovariectomized adult female cynomolgus monkeys were fed a moderately atherogenic diet for 12 weeks with either oral conjugated equine estrogen ([CEE] n = 8), medroxyprogesterone acetate ([MPA] n = 9), or combined CEE + MPA (n = 9) and compared with a control group (n = 8) that did not receive exogenous sex hormones. After 12 weeks, hepatic cholesterol was significantly lower in CEE-treated (6.2 +/- 1.2 mg/g liver) and CEE + MPA-treated (6.4 +/- 0.9 mg/g liver) animals compared with the control (12.6 +/- 1.9 mg/g liver) and MPA-treated (14.6 +/- 1.6 mg/g liver) groups. Hepatic cholesterol 7alpha-hydroxylase mRNA abundance was significantly increased in CEE-treated (0.553 +/- 0.08 pg/microg RNA), MPA-treated (0.734 +/- 0.12 pg/microg RNA), and CEE + MPA-treated (0.487 +/- 0.07 pg/microg RNA) animals compared with the controls (0.318 +/- 0.03 pg/microg RNA). There was no significant difference in the plasma LDL cholesterol concentration and hepatic LDL receptor mRNA abundance between the groups. These data support but do not prove the hypothesis that low-dose oral estrogen induces an increase in cholesterol 7alpha-hydroxylase mRNA abundance, which is correlated with biliary cholesterol secretion and may result in depletion of hepatic cholesterol.

Animals↗

PubMed1996

Estrogen increases low-density lipoprotein receptor-independent catabolism of apolipoprotein B in hyperlipidemic rabbits.

Estrogen has been reported to increase the catabolism of low-density lipoprotein (LDL) apolipoprotein (apo) B by increasing LDL receptor activity. To determine the effect of estrogen on LDL receptor-independent pathways, paired turnover studies of native LDL and chemically modified LDL (methyl-LDL) were performed before and during estrogen administration in female New Zealand rabbits consuming a diet containing 0.5% (wt/wt) cholesterol. Rabbits were matched by plasma cholesterol concentration and assigned randomly to receive estrogen (estradiol cypionate 0.5 mg/kg/wk) or placebo. The residence time of both the native LDL apo B tracer and the methyl-LDL apo B tracer in plasma was decreased by estrogen but not by placebo. Multicompartmental modeling of the paired, double-labeled turnover studies indicated that an increase in fractional catabolic rate (FCR) of the fast-turnover pool, a kinetically distinct LDL subpopulation in plasma, accounted for the observed decrease in residence time in plasma for both tracers. These data support the hypothesis that, in addition to any effect on the LDL receptor, estrogen promotes the activity of LDL receptor-independent pathways.

Animals↗

PubMed1994

Plasma low density lipoprotein cholesterol concentration in cynomolgus monkeys; differing effects of age and body weight in animals consuming low and high cholesterol diets.

It has been reported in cross-sectional studies that plasma cholesterol concentration does not increase with age in nonhuman primates who consume a cholesterol-free diet over their lifetimes. However, dietary composition and body weight may confound any change in plasma cholesterol concentration during aging, as is the case in humans in industrialized societies. To determine if the relationship between age and plasma cholesterol concentration is affected by dietary cholesterol and body weight in nonhuman primates, we compared post-pubertal male cynomolgus monkeys consuming low cholesterol (0.04 mg cholesterol/kcal; n = 10) and high cholesterol (0.39 mg cholesterol/kcal: n = 21) diets. A univariate repeated measures analysis of covariance of low density lipoprotein (LDL) cholesterol concentration was performed from a longitudinal data set (monkeys aged 5 to 20 years), containing an average of 34 observations per animal. The interaction of age and body weight on LDL cholesterol concentration differed among the two dietary groups. In monkeys consuming the low cholesterol diet, an increase in age was associated with a small increase in mean LDL cholesterol concentration. This effect of age increased with increasing body weight. Monkeys on the high cholesterol diet had higher mean LDL concentration, but showed no significant effect of aging on concentration. Instead, at all ages, LDL concentration was strongly affected (positively) by body weight in this group. A qualitatively similar (but quantitatively smaller) effect of body weight was observed only at older ages in the low dietary cholesterol group. We conclude that the associations of LDL concentration with age and body weight in cynomolgus monkeys are strongly influenced by dietary cholesterol.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗

PubMed1994

The "peripneumonia" period in the older adult.

CAP in the older adult is a complex multifactorial syndrome. Older adults are at increased risk for pneumonia and death associated with pneumonia. The prevalence and severity of risk factors for pneumonia increase with age. Although alterations in respiratory function occur with increased frequency in the elderly, immune senescence is probably the major predisposing factor contributing to the increased incidence, morbidity, and mortality of respiratory infection in the elderly. Yet, risk factors, once identified, may be amendable to interventions and health behavior modification to reduce the occurrence of pneumonia. Older patients discharged from the hospital after recovering from pneumonia are at increased risk for subsequent hospitalizations and death. Further studies are needed to explore the long-term consequences of pneumonia in the antimicrobial era on quality of life and physical and psychosocial functioning.

Aged↗

PubMed1993

Oral contraceptives decrease hepatic cholesterol independent of the LDL receptor in nonhuman primates.

Pharmacological doses of estrogens have been reported to increase hepatic catabolism of low-density lipoprotein (LDL) by the LDL receptor (LDL-R) pathway and to increase the concentration of mRNA for the LDL receptor. The induction of LDL-Rs by large doses of estrogen may not be relevant to the role of estrogens under physiological conditions. Furthermore, the mechanisms by which oral contraceptives, a combination of synthetic estrogen and progestin, may modulate LDL metabolism remain largely unexplored. Adult female cynomolgus monkeys were given combination ethinyl estradiol/norgestrel preparations (n = 16) for 16 weeks and were compared with a control group that did not receive exogenous sex hormones (n = 7). All animals consumed a diet containing 0.25 mg cholesterol/kcal with 40% of calories from saturated fats. After 16 weeks of treatment there was no significant difference in LDL cholesterol (LDL-C) and hepatic LDL-R mRNA concentration between oral contraceptive-treated animals (LDL-C, 242 +/- 113 mg/dL; LDL-R mRNA, 0.60 +/- 0.31 pg/microgram RNA) and control animals (LDL-C, 277 +/- 100 mg/dL; LDL-R mRNA, 0.51 +/- 0.21 pg/microgram RNA). In contrast, the hepatic cholesteryl ester concentration was significantly lower in the oral contraceptive-treated animals (7.28 +/- 3.59 mg/g liver) compared with the control animals (16.07 +/- 11.86 mg/g liver; P = .01) with no significant difference in hepatic free cholesterol concentration between the groups. Thus, oral contraceptives decrease hepatic cholesterol concentration independent of LDL-R expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

A dose-response relationship between sex hormone-induced change in hepatic triglyceride lipase and high-density lipoprotein cholesterol in postmenopausal women.

In previous studies, we have demonstrated a temporal relationship between the postheparin hepatic triglyceride lipase (HTGL) response to sex steroids and the high-density lipoprotein (HDL) cholesterol response. To determine if this relationship is dose-dependent, we compared the effect of three graduated doses of orally administered estradiol and norgestrel in two groups of six postmenopausal women. With estradiol administration, postheparin HTGL activity decreased from 91 +/- 46 to 50 +/- 29 nmol/min/mL, baseline to high dose (P less than .05); HDL cholesterol increased from 54 +/- 6 to 64 +/- 10 mg/dL (P less than .05); HDL2 cholesterol increased from 16 +/- 4 to 23 +/- 7 mg/dL (P less than .05); and HDL3 cholesterol concentration did not change. With norgestrel administration, HTGL activity increased from 79 +/- 19 to 109 +/- 24 nmol/min/mL (P less than .05); HDL cholesterol decreased from 64 +/- 17 to 43 +/- 7 mg/dL (P less than .05); HDL2 cholesterol decreased from 21 +/- 17 to 6 +/- 5 mg/dL (P less than .05); and HDL3 cholesterol concentration decreased from 43 +/- 8 to 38 +/- 8 mg/dL (P less than .05). The HTGL activity response was inversely correlated with estrogen dose (rs = -.733, P = .0001) and directly correlated with progestin dose (rs = .895, P = .0001). The HDL cholesterol response was directly correlated with estrogen dose (HDL: rs = .741, P = .001; HDL2: rs = .586, P = 0.003) and inversely correlated with progestin dose (HDL: rs = -.933, P = .0001; HDL2: rs = -.866, P = .0001; HDL3: rs = -.576, P = .003).(ABSTRACT TRUNCATED AT 250 WORDS)

Cholesterol, HDL↗

PubMed1990

Differential effects of oral estrone versus 17 beta-estradiol on lipoproteins in postmenopausal women.

Toward the definition of optimal postmenopausal estrogen replacement we compared the effects of three graduated doses of two oral estrogens, estrone sulfate and 17 beta-estradiol, on the lipid profiles of two groups of six postmenopausal women. Because of metabolic interconversions equivalent serum concentrations of estrone and estradiol were produced with these regimens. However, differential effects were noted in lipoproteins. 17 beta-Estradiol caused an increase in total plasma cholesterol (from 5.71 +/- 0.36 to 5.99 +/- 0.57 mmol/L, baseline to high dose; P less than 0.02), high density lipoprotein (HDL) cholesterol (from 1.45 +/- 0.15 to 1.78 +/- 0.36 mmol/L; P less than 0.02), HDL2 cholesterol concentration (from 0.41 +/- 0.08 to 0.62 +/- 0.26 mmol/L; P less than 0.01), and triglyceride concentration (from 1.09 +/- 0.29 to 1.24 +/- 0.30 mmol/L; P less than 0.01) without affecting low density lipoprotein (LDL) cholesterol concentration. By contrast, estrone sulfate caused a decrease in total plasma cholesterol (from 6.51 +/- 0.85 to 5.87 +/- 0.41 mmol/L; P less than 0.05) and LDL cholesterol concentration (from 4.34 +/- 0.57 to 3.67 +/- 0.44 mmol/L; P less than 0.01) and an increase in HDL cholesterol (from 1.37 +/- 0.20 to 1.50 +/- 0.26 mmol/L; P less than 0.05) and HDL2 cholesterol concentration (from 0.34 +/- 0.18 to 0.49 +/- 0.18 mmol/L; P less than 0.01), but no change in total triglyceride concentration. We deduce that the differential effect of orally administered estrogens on lipoprotein metabolism in postmenopausal women may be attributed to a first pass effect on hepatic metabolism.

Administration, Oral↗

PubMed1977

Quinazolines as inhibitors of dihydrofolate reductase. 4. Classical analogues of folic and isofolic acids.

A series of classical quinazoline analogues of folic and isofolic acids was evaluated for inhibitory activity against the dihydrofolate reductases from rat liver and from Streptococcus faecium. Included in this group were the known active antitumor agents methasquin and chlorasquin as well as methotrexate. Two new compounds, N10-formyl-5,8-deazaaminopterin and N10-formyl-5,8-deazafolic acid, were synthesized specifically for this study. The latter displayed modest activity against L1210 leukemia in mice.

Animals↗