Biomedical subjects

Zhensheng Li

Publications and source records attributed to Zhensheng Li.

10 recordsLinked to original sources

PubMed2006

Characterization of photosynthesis of flag leaves in a wheat hybrid and its parents grown under field conditions.

Two wheat cultivars, one with high yield and the other with a high tolerance against oxidative stress, were compared with a hybrid of these two cultivars by investigating their photosynthetic characteristics of flag leaves. From the beginning of flowering to the 17th day, CO(2) assimilation rate (P(max)) was maintained and there were no appreciable differences between the hybrid and its parents. P(max) showed no decrease at noon compared to that in the morning. From the 20th to the 30th day of flowering, P(max) decreased significantly, and this decrease was significantly less in the hybrid than in its parents. The actual photosystem II (PSII) efficiency (Phi(PSII)) and the maximal efficiency of PSII photochemistry (F(v)/F(m)) showed a significant decrease only on the 30th day after anthesis; this decline was much less marked in the hybrid relative to its parents, both in the morning and at noon. A decrease occurred in Phi(PSII) and F(v)/F(m) at noon when compared to that in the morning, but this decrease was less marked in the hybrid than in its parents. Rubisco activity decreased significantly from the 13th day of flowering and was higher in the morning than at noon both in the hybrid and its parents. However, the hybrid always showed a higher value of Rubisco activity. The activities of posphoenolpyruvate carboxylase and pyruvate phosphate dikinase showed similar changes to those in Rubisco activity, particularly from the 20th to 30th day. The results of this study suggest that the higher photosynthetic capacity of the flag leaf in the hybrid can help to accumulate more dry material, and may be the physiological basis for higher yield over its parents.

Biomass↗

PubMed2006

The epidemiology of systolic blood pressure and death risk in hemodialysis patients.

BACKGROUND: This study compares the associations of predialysis systolic blood pressure (SBP) with mortality risk in both incident and prevalent hemodialysis (HD) cohorts by using both conventional and time-varying Cox analyses, thus addressing limitations of prior studies. METHODS: A total of 56,338 incident patients starting HD therapy during 1997 to 2001 and 69,590 prevalent HD patients on January 1, 2002, were grouped into the following categories: (1) SBP less than 120 mm Hg, (2) 120 < or = SBP < 140 mm Hg, (3) 140 < or = SBP < 160 mm Hg, (4) 160 < or = SBP < 180 mm Hg, (5) 180 < or = SBP < 200 mm Hg, and (6) SBP of 200 mm Hg or greater. Conventional and time-varying models evaluated 1-year and 3-year (incident patients only) survival. RESULTS: Nine percent and 26.0% of incident patients and 5.7% and 20.1% of prevalent patients were in categories 1 and 2, respectively. Their associated 1-year hazard ratios (HRs) were 2.63 to 3.68 and 1.57 to 1.68 compared with category 4, the reference group. HRs for categories 3, 5, and 6 were not different from category 4. Time-varying models magnified category 1 and 2 HRs to 5.54 to 7.42 and 1.92 to 2.21, such that 25% to 35% of patients in the target SBP range (< 140 mm Hg) had the greatest risk. A "reversed J-shaped" risk profile emerged in the time-varying models, with very high SBP (category 6) associated with HRs of 1.52 to 1.55, but only 1% of patients were in category 6. Three-year outcomes were similar. CONCLUSION: Epidemiological characteristics of predialysis SBP consistently differ from those in the general population despite different analytic perspectives. The data suggest a need for greater investigative, diagnostic, and therapeutic focus on HD patients with normal and prehypertensive blood pressure ranges.

Blood Pressure↗

PubMed2006

Physical mapping of the blue-grained gene(s) from Thinopyrum ponticum by GISH and FISH in a set of translocation lines with different seed colors in wheat.

The original blue-grained wheat, Blue 58, was a substitution line derived from hybridization between common wheat (Triticum aestivum L., 2n=6x=42, ABD) and tall wheatgrass (Thinopyrum ponticum Liu & Wang=Agropyron elongatum, 2n=10x=70, StStEeEbEx), in which one pair of 4D chromosomes was replaced by a pair of alien 4Ag chromosomes (unknown group 4 chromosome from A. ponticum). Blue aleurone might be a useful cytological marker in chromosome engineering and wheat breeding. Cytogenetic analysis showed that blue aleurone was controlled by chromosome 4Ag. GISH analysis proved that the 4Ag was a recombination chromosome; its centromeric and pericentromeric regions were from an E-genome chromosome, but the distal regions of its two arms were from an St-genome chromosome. On its short arm, there was a major pAs1 hybridization band, which was very close to the centromere. GISH and FISH analysis in a set of translocation lines with different seed colors revealed that the gene(s) controlling the blue pigment was located on the long arm of 4Ag. It was physically mapped to the 0.71-0.80 regions (distance measured from the centromere of 4Ag). The blue color is a consequence of dosage of this small chromosome region derived from the St genome. We speculate that the blue-grained gene(s) could activate the anthocyanin biosynthetic pathway of wheat.

Chromosomes, Plant↗

PubMed2005

Chitosan-alginate as scaffolding material for cartilage tissue engineering.

Tissue compatibility of chitosan-alginate scaffolds was studied in vitro in terms of cell morphology, proliferation, and functionality using HTB-94 cells. The scaffold has an interconnected 3D porous structure, and was fabricated by thermally induced phase separation followed by freeze drying. Cell proliferation on the chitosan-alginate scaffold was found to be faster than on a pure chitosan scaffold. After cell culture for 2 weeks in vitro, the cells on the chitosan scaffold gradually assumed a fibroblast-like morphology while the cells on the chitosan-alginate scaffold retained their spherical morphology throughout the period of study. SDS-PAGE electrophoresis and Western blot assays for proteins extracted from cells grown on scaffolds indicated that production of cartilage-specific collagen type II, a marker for chondrocytic phenotype, increased from week 2 to week 3 on the chitosan-alginate scaffold but decreased on the chitosan scaffold. This study suggested that chitosan-alginate scaffolds promote cell proliferation, enhance phenotype expression of HTB-94 chondrocytes, and may potentially serve as an improved alternative to chitosan scaffolds for cartilage tissue engineering.

Alginates↗

PubMed2005

Chitosan-alginate hybrid scaffolds for bone tissue engineering.

A biodegradable scaffold in tissue engineering serves as a temporary skeleton to accommodate and stimulate new tissue growth. Here we report on the development of a biodegradable porous scaffold made from naturally derived chitosan and alginate polymers with significantly improved mechanical and biological properties as compared to its chitosan counterpart. Enhanced mechanical properties were attributable to the formation of a complex structure of chitosan and alginate. Bone-forming osteoblasts readily attached to the chitosan-alginate scaffold, proliferated well, and deposited calcified matrix. The in vivo study showed that the hybrid scaffold had a high degree of tissue compatibility. Calcium deposition occurred as early as the fourth week after implantation. The chitosan-alginate scaffold can be prepared from solutions of physiological pH, which may provide a favorable environment for incorporating proteins with less risk of denaturation. Coacervation of chitosan and alginate combined with liquid-solid separation provides a scaffold with high porosity, and mechanical and biological properties suitable for rapid advancement into clinical trials.

Alginates↗

PubMed2005

A two-component high-affinity nitrate uptake system in barley.

The analysis of genome databases for many different plants has identified a group of genes that are related to one part of a two-component nitrate transport system found in algae. Earlier work using mutants and heterologous expression has shown that a high-affinity nitrate transport system from the unicellular green algae, Chlamydomonas reinhardtii required two gene products for function. One gene encoded a typical carrier-type structure with 12 putative trans-membrane (TM) domains and the other gene, nar2 encoded a much smaller protein that had only one TM domain. As both gene families occur in plants we investigated whether this transport model has more general relevance among plants. The screening for nitrate transporter activity was greatly helped by a novel assay using (15)N-enriched nitrate uptake into Xenopus oocytes expressing the proteins. This assay enables many oocytes to be rapidly screened for nitrate transport activity. The functional activity of a barley nitrate transporter, HvNRT2.1, in oocytes required co-injection of a second mRNA. Although three very closely related nar2-like genes were cloned from barley, only one of these was able to give functional nitrate transport when co-injected into oocytes. The nitrate transport performed by this two-gene system was inhibited at more acidic external pH and by acidification of the cytoplasm. This specific requirement for two-gene products to give nitrate transport function has important implications for attempts to genetically manipulate this fundamental process in plants.

Amino Acid Sequence↗

PubMed2005

The online measurement of hemodialysis dose (Kt): clinical outcome as a function of body surface area.

BACKGROUND: Recent advances enable the direct measurement of small molecule clearance, Kecn, during each dialysis. Average Kecn and treatment length, t, are multiplied giving total clearance, Kt. The body surface area (BSA) is a fixed transformation of height and weight and is a well recognized measure of body size. This project was conceived to search for clinical outcome-based functions for measured Kt in terms of BSA to enable simple Kt prescription guidelines for clinicians who are able to measure Kecn, and to provide foundations for future clinical research. METHODS: The data came from Fresenius Medical Care (NA) files and included more than 32,000 patients with height, weight, and paired Kecn and t measurements during December 2002. Measurements were averaged for the month and used as predictor measures in Cox models of survival time during 2003. Candidate Kt values from 30 L/treatment through 70 were examined to determine the best statistical fit for quintile and decile delimited BSA groups evaluating the best fit Kt treatment target for each group. Functional forms representing the relationship between target Kt values and mean BSA of the groups were then evaluated to determine the best fit. RESULTS: Kt targets increased with BSA in a curvilinear way such that the rate of increase is greater at low BSA than high. The best statistical fit was a double reciprocal form, Kt = 1/(a + b/BSA); "a" and "b" are statistically derived coefficients. The form has an appealing mathematical property; Kt approaches 0 as BSA approaches 0. Other forms fit the data nearly as well, however, and can be used to estimate Kt targets for patients with different BSA. CONCLUSION: Empirical, outcome-based functions of measured Kt in terms of BSA exist and can be used as aids for prescribing and judging hemodialysis treatment.

Aged↗

PubMed2004

Reprocessing dialysers for multiple uses: recent analysis of death risks for patients.

BACKGROUND: Reprocessing dialysers is a common cost-saving practice in the USA. It began when patients were treated with bio-incompatible cellulosic membranes that were associated with medical complications, but has continued for economic reasons despite the current use of more biocompatible non-cellulosic membranes. A dialysis services and product provider using primarily its own non-cellulosic membranes recently embarked on a staged programme to stop reprocessing dialysers. Approximately a quarter of 71,000 patients had been switched from reuse to single use by July 1, 2001. The transition offered a unique opportunity to re-evaluate death risk associated with the reuse practice. METHODS: Patients were classified as reuse or single use as of July 1, 2001. Survival time measurements started on that date (Lag0) and at four 30 day intervals after it (Lag30, Lag60, Lag90 and Lag120). Thus, patients must have been treated in their reuse group after Lag0 for at least 30, 60, 90 or 120 days, respectively. Survival time was evaluated during 1 year following the lag date using the Cox method in unadjusted, case mix-adjusted and case mix plus other measure-adjusted models. RESULTS: All analyses suggested favourable survival advantage among patients treated with single use dialysers. The differences were statistically significant at all lag times in the unadjusted models but became significant only at later lag times in the case mix- and case mix plus other measure-adjusted models. For example, single use/reuse hazard ratios in the case mix-adjusted models at Lag0-Lag120 were 0.96 (NS), 0.96 (NS), 0.94 (P = 0.02), 0.93 (P = 0.02) and 0.92 (P = 0.01), respectively. CONCLUSIONS: A risk benefit appears associated with abandonment of the dialyser reuse practice, although the benefit may lag behind the change. In the USA, the relative risk burden associated with the reprocessing of dialysers may have changed over time with the evolution of clinical practice.

Aged↗

PubMed2004

Measurement of dialyzer clearance, dialysis time, and body size: death risk relationships among patients.

BACKGROUND: Urea pharmacokinetic equation systems have contributed to better understanding of treatment dose among hemodialysis patients. The methods are indirect, however, and require the measurement of blood urea nitrogen (BUN) concentration before and after a dialysis session to estimate the total treatment dose that clinicians prescribe [urea clearance x dialysis time (Kt)] indexed to an estimate of body size [the volume of urea distribution in the body (V)] yielding the ratio, Kt/V. New technology permits direct on-line measurement of average small molecule clearance (Kecn) during each dialysis treatment that can be multiplied by time (t) to give a direct measurement of total treatment dose (Kt). This study evaluated the relationship of measured Kt with death risk. It also evaluated the relationship of simple body size measures to risk and also the combination of one such measure [body surface area (BSA)] with Kt to death risk. METHODS: The data were taken from the Fresenius Medical Care (NA) (FMCNA) clinical database that included patients who had outcome data, height and weight measurements, and at least one average Kecn and t measurement during April 2002. Kecn, t, and the body size measures [body weight, body mass index (BMI), and BSA)] were averaged during the month. Those values were used as predictors of survival during the next 1 year in unadjusted and case mix adjusted proportional hazards (Cox) models. RESULTS: Increasing values of Kecn, t, Kt and all of the body size measures were associated with lower death risk. The body size measure most closely associated with risk was the BSA that was used in subsequent models. Kt and BSA were independent risk predictors. There was a significant interaction between Kt and BSA in the case mix but not the unadjusted model indicating that the risk burden of lower total dialysis dose, Kt, may be greater among small than large patients. CONCLUSION: The direct measurement of dialysis dose during each treatment is practical and the values reported by it are clinically relevant. Higher dose was associated with better survival in both small and large patients treated three times weekly. Furthermore, smaller patients may require proportionately greater total dose than larger patients to achieve comparable survival.

Aged↗

PubMed2002

Body size, dialysis dose and death risk relationships among hemodialysis patients.

BACKGROUND: The normalized treatment ratio, Kt/V derived from urea kinetic models (UKM), is a commonly used measure of dialysis dose. This measure assumes that smaller patients with low volume of urea distribution (V) require proportionately less total treatment (Kt) than larger patients. The conclusion has been questioned because the UKM use assumptions that could make them invalid for accurately predicting a clinical outcome like survival. It is possible that a relationship exists between Kt and body size whereby a different Kt is required for different sizes. This study therefore explored the relationships among body size, Kt, and death risk focusing on possible interactions between Kt and size. METHODS: The sample included 43,334 patients treated on January 1, 1999. Survival time was modeled using Kt or body size groups to evaluate the shape of the risk profiles. Kt and the size measures were then evaluated together as continuous functions both in main effects (that is, Kt and size) and interaction models to see if the association of Kt with risk might be different for different sizes. The size measures were body weight, weight adjusted statistically for height, body surface area (BSA), weight divided by height (wt/ht) and the body mass index (BMI). RESULTS: The log of risk decreased in rough linear fashion for Kt, weight, weight for height, and BSA. The log-risk relationships were "reverse J-shaped" for wt/ht and BMI. The main effects models suggested improved survival with increasing Kt and all of the size measures. Adding an interaction term increased the benefit associated with increasing Kt and for weight, weight for height and BSA at low values of Kt and size. A significant, positive interaction term mitigated those effects at higher values. Thus, the death risk penalties associated with reducing Kt among small patients were as great as or greater than they were among large patients. A similar pattern was observed for V. Adding the interaction to the BMI model destroyed the main effects, so that there was no significant association between risk and either Kt or BMI. A cross-categorical model of BMI and Kt, however, revealed improving survival with increasing Kt among both low and high BMI patients throughout the range of Kt. CONCLUSIONS: Evidence supporting the intuition that smaller patients require proportionately lower dialysis dose than larger patients was not found. To the contrary, smaller patients suffer as much risk as or more risk than larger patients from reducing Kt. Deciding dialysis treatment using a Kt/V based intuition may lead to avoidable under-dialysis particularly among small patients.

Adult↗