Biomedical subjects

Michael Liebman

Publications and source records attributed to Michael Liebman.

9 recordsLinked to original sources

PubMed2005

Exploring human plasma proteome strategies: high efficiency in-solution digestion protocol for multi-dimensional protein identification technology.

Multi-dimensional protein identification technology (MudPIT) is becoming a prevalent proteomic approach due to its high-throughput separations and accurate mass detection. Prior to MudPIT analysis, complicated samples required in-solution digestion. Unlike in-gel digestion, in which enzymes work on just a few proteins, in-solution digestion involves simultaneous digestion of hundreds or thousands of proteins. In-solution digestion protocols must therefore be very efficient. Few investigations have evaluated the efficiency of in-solution digestion protocols. The present research compared three such protocols. Results suggest that a protocol utilizing trifluoroethanol (TFE) as denaturant is most efficient.

Blood Proteins↗

PubMed2005

Proteomic profiling of human urine using multi-dimensional protein identification technology.

Human urine samples are ideal for proteomic profiling and have tremendous potential as sources of biomarkers. Multi-dimensional protein identification technology (MudPIT) is an effective approach to analyzing human urine or other fluids dominated by diverse metabolites. MudPIT analysis was used to identify 87 proteins in just 15 ml of human urine. A high throughput, reproducible, and sensitive technology, MudPIT may soon be used for more proteomic analyses of metabolites.

Humans↗

PubMed2005

Effect of different cooking methods on vegetable oxalate content.

Approximately 75% of all kidney stones are composed primarily of calcium oxalate, and hyperoxaluria is a primary risk factor for this disorder. Nine types of raw and cooked vegetables were analyzed for oxalate using an enzymatic method. There was a high proportion of water-soluble oxalate in most of the tested raw vegetables. Boiling markedly reduced soluble oxalate content by 30-87% and was more effective than steaming (5-53%) and baking (used only for potatoes, no oxalate loss). An assessment of the oxalate content of cooking water used for boiling and steaming revealed an approximately 100% recovery of oxalate losses. The losses of insoluble oxalate during cooking varied greatly, ranging from 0 to 74%. Because soluble sources of oxalate appear to be better absorbed than insoluble sources, employing cooking methods that significantly reduce soluble oxalate may be an effective strategy for decreasing oxaluria in individuals predisposed to the development of kidney stones.

Beta vulgaris↗

PubMed2005

Ascorbate increases human oxaluria and kidney stone risk.

Currently, the recommended upper limit for ascorbic acid (AA) intake is 2000 mg/d. However, because AA is endogenously converted to oxalate and appears to increase the absorption of dietary oxalate, supplementation may increase the risk of kidney stones. The effect of AA supplementation on urinary oxalate was studied in a randomized, crossover, controlled design in which subjects consumed a controlled diet in a university metabolic unit. Stoneformers (n = 29; SF) and age- and gender-matched non-stoneformers (n = 19; NSF) consumed 1000 mg AA twice each day with each morning and evening meal for 6 d (treatment A), and no AA for 6 d (treatment N) in random order. After 5 d of adaptation to a low-oxalate diet, participants lived for 24 h in a metabolic unit, during which they were given 136 mg oxalate, including 18 mg 13C2 oxalic acid, 2 h before breakfast; they then consumed a controlled very low-oxalate diet for 24 h. Of the 48 participants, 19 (12 stoneformers, 7 non-stoneformers) were identified as responders, defined by an increase in 24-h total oxalate excretion > 10% after treatment A compared with N. Responders had a greater 24-h Tiselius Risk Index (TRI) with AA supplementation (1.10 +/- 0.66 treatment A vs. 0.76 +/- 0.42 treatment N) because of a 31% increase in the percentage of oxalate absorption (10.5 +/- 3.2% treatment A vs. 8.0 +/- 2.4% treatment N) and a 39% increase in endogenous oxalate synthesis with treatment A than during treatment N (544 +/- 131 A vs. 391 +/- 71 micromol/d N). The 1000 mg AA twice each day increased urinary oxalate and TRI for calcium oxalate kidney stones in 40% of participants, both stoneformers and non-stoneformers.

Adult↗

PubMed2004

Oxalate absorption and endogenous oxalate synthesis from ascorbate in calcium oxalate stone formers and non-stone formers.

BACKGROUND: Increased rates of either oxalate absorption or endogenous oxalate synthesis can contribute to hyperoxaluria, a primary risk factor for the formation of calcium oxalate-containing kidney stones. This study involves a comparative assessment of oxalate absorption and endogenous oxalate synthesis in subpopulations of stone formers (SFs) and non-stone formers (NSFs) and an assessment of the effect of ascorbate supplementation on oxalate absorption and endogenous oxalate synthesis. METHODS: Twenty-nine individuals with a history of calcium oxalate kidney stones (19 men, 10 women) and 19 age-matched NSFs (8 men, 11 women) participated in two 6-day controlled feeding experimental periods: ascorbate-supplement (2 g/d) and no-supplement treatments. An oxalate load consisting of 118 mg of unlabeled oxalate and 18 mg of 13C2 -oxalic acid was administered the morning of day 6 of each experimental period. RESULTS: Mean 13C2 -oxalic acid absorption averaged across the ascorbate and no-supplement treatments was significantly greater in SFs (9.9%) than NSFs (8.0%). SFs also had significantly greater 24-hour post-oxalate load urinary total oxalate and endogenous oxalate levels with both treatments. Twenty-four-hour urinary total oxalate level correlated strongly with both 13C2 -oxalic acid absorption (SFs, r = 0.76; P < 0.01; NSFs, r = 0.62; P < 0.01) and endogenous oxalate synthesis (SFs, r = 0.95; P < 0.01; NSFs, r = 0.92; P < 0.01). CONCLUSION: SFs are characterized by greater rates of both oxalate absorption and endogenous oxalate synthesis, and both these factors contribute to the hyperoxaluric state. The finding that ascorbate supplementation increased urinary total and endogenous oxalate levels suggested that this practice is a risk factor for individuals predisposed to kidney stones.

Adult↗

PubMed2004

Assessment of oxalate absorption from almonds and black beans with and without the use of an extrinsic label.

PURPOSE: Oxalate bioavailability is an important determinant of whether the consumption of a particular food is a high risk in individuals predisposed to kidney stones. We estimated and compared oxalate absorption from a high oxalate containing legume (black beans) and a high oxalate containing nut (almonds). We also compared an isotope method using extrinsically labeled oxalate and an oxalate load method to assess oxalate absorption. MATERIALS AND METHODS: Six male and 5 female subjects participated in the 4 oxalate load tests, namely almonds, almonds with 20 mg C2-oxalic acid, black beans and black beans with 20 mg C2-oxalic acid. Each treatment provided a total of 120 mg oxalate, after which timed urine samples were collected for the analysis of oxalate, calcium and creatinine. RESULTS: Average oxalate absorption from the 2 almond treatments (5.9%) using the oxalate load method was significantly higher than that from the 2 black bean treatments (1.8%) during the 24-hour post-oxalate load collection period. In contrast, C2-oxalic acid absorption from the almond (7.9%) and black bean (8.6%) treatments did not significantly differ. CONCLUSIONS: The higher oxalate absorption from almonds than from black beans suggests that the relative amount of soluble and insoluble oxalate in food has an important role in the determination of oxalate absorption. Since extrinsically provided C2-oxalate and oxalate naturally occurring in the high oxalate test foods appeared to be differentially absorbed, the data do not support the use of extrinsically labeled oxalate to assess food oxalate absorption.

Adult↗

PubMed2003

1-Mb resolution array-based comparative genomic hybridization using a BAC clone set optimized for cancer gene analysis.

Array-based comparative genomic hybridization (aCGH) is a recently developed tool for genome-wide determination of DNA copy number alterations. This technology has tremendous potential for disease-gene discovery in cancer and developmental disorders as well as numerous other applications. However, widespread utilization of a CGH has been limited by the lack of well characterized, high-resolution clone sets optimized for consistent performance in aCGH assays and specifically designed analytic software. We have assembled a set of approximately 4100 publicly available human bacterial artificial chromosome (BAC) clones evenly spaced at approximately 1-Mb resolution across the genome, which includes direct coverage of approximately 400 known cancer genes. This aCGH-optimized clone set was compiled from five existing sets, experimentally refined, and supplemented for higher resolution and enhancing mapping capabilities. This clone set is associated with a public online resource containing detailed clone mapping data, protocols for the construction and use of arrays, and a suite of analytical software tools designed specifically for aCGH analysis. These resources should greatly facilitate the use of aCGH in gene discovery.

Cell Line, Tumor↗

PubMed2002

Biomarkers of bone health appropriate for evaluating functional foods designed to reduce risk of osteoporosis.

Osteoporosis is a growing global problem. The health care costs and decreased productivity and quality of life are staggering. Much research is invested in life-style approaches to build peak bone mass during growth to prevent osteoporosis as well as to treat the disease in later life. Functional foods have enjoyed a niche in bone health. Foods fortified with Ca are most popular. Other bone nutrients such as vitamin D, Mg and vitamin K are sometimes added. Future products are likely to include enhancers of Ca absorption such as inulin or whey proteins. Dietary factors that reduce urinary Ca loss (plant proteins) or suppress bone resorption (possibly phyto-oestrogens) are also gaining attention. Methodologies for evaluating the effectiveness of functional foods on bone health include measures of bone quality such as bone densitometry or measures of Ca metabolism, particularly absorption. Biochemical markers for bone turnover are less satisfactory for diet-related effects. Use of a rare isotope, 41Ca, and accelerator mass spectrometry offers a new approach for assessing the ability of functional foods to suppress bone resorption.

Biomarkers↗

PubMedDate not supplied

Promoting healthy weight: lessons learned from WIN the Rockies and other key studies.

In contrast to the traditional weight-centered approach, the Health At Every Size (HAES) or nondieting approach is health centered, with no focus on losing a predetermined amount of weight or fat. A key HAES principle of advocating healthy changes in food selection rather than adherence to prescriptive diets that involve calorie counting was adopted by Wellness in the Rockies (WIN the Rockies), a community-based research, intervention, and outreach project that promoted healthy lifestyles related to food, physical activity, and body image at the individual and community levels in Wyoming, Montana, and Idaho. The results from the project's cross-sectional surveys indicated that increased frequency of eating food while doing another activity, of drinking sweetened beverages such as soft drinks, and of consuming foods from fast-food restaurants were significant predictors of a high body mass index (BMI). In terms of energy expenditure, other predictors of high BMI from the WIN the Rockies cross-sectional surveys were lower frequency of participation in physical activity and the perception of not getting as much exercise as needed. The overall data provide support for the view that small diet- and physical activity-related lifestyle changes can cumulatively make a significant contribution to maintenance of healthy body weights. Although the community intervention emphasis of WIN the Rockies did not allow a specific assessment of the efficacy of HAES for individual participants in the project, this approach appears to hold great potential for promoting healthful lifestyle changes that improve quality of life.

Body Image↗