David W. Johnson

Bio: David W. Johnson is an academic researcher from University of Queensland. The author has contributed to research in topics: Peritoneal dialysis & Kidney disease. The author has an hindex of 160, co-authored 2714 publications receiving 140778 citations. Previous affiliations of David W. Johnson include Minnesota Department of Transportation & Open University.

Isolation, propagation and characterization of primary tubule cell culture from human kidney.

Abstract: Proximal tubule cells (PTC) are the major cell type in the cortical tubulointerstitium. Because PTC play a central role in tubulointerstitial pathophysiology, it is essential to prepare pure PTC from kidney tissue to explore the mechanisms of tubulointerstitial pathology. The authors have successfully refined and characterized primary cultures of human PTC using Percoll density gradient centrifugation as a key PTC enrichment step. The cells obtained by this method retain morphological and functional properties of PTC and are minimally contaminated by other renal cells. In particular, the primary isolates have characteristics of epithelial cells with uniform polarized morphology, tight junction and well-formed apical microvilli. Cytokeratin is uniformly and strongly expressed in the isolates. Brush border enzyme activities and PTC transport properties are retained in the isolates. This method therefore provides an excellent in vitro model for the physiologic study of the human proximal tubule.

Erythropoietin protects against apoptosis and increases expression of non-neuronal cell markers in the hypoxia-injured developing brain.

Abstract: Erythropoietin (EPO) is a cytokine hormone with cytoprotective effects in many tissues including the brain. Although the benefits of administration of recombinant human EPO (rhEPO) for neonatal hypoxic brain injury have been demonstrated in neuronal tissue, the effect on non-neuronal cell populations is unclear. We tested the hypothesis that rhEPO would not only protect neuronal cells but also glial cells at a stage of brain development where their maturation was particularly sensitive, and also protect the vasculature. This was evaluated in a rat model of hypoxic injury. 1000 IU/kg rhEPO was delivered intraperitoneally at the start of 4 h hypoxia or normoxia. Treatment groups of neonatal rats (day of birth, at least N = 10 per group) were as follows: normoxia; normoxia plus rhEPO; hypoxia (8% FiO(2) delivered in temperature-controlled chambers); and hypoxia plus rhEPO. Day of birth in rats is equivalent to human gestation of 28-32 weeks. The effects of rhEPO administration, especially to non-neuronal cell populations, and the associated molecular pathways, were investigated. Apoptosis was increased with hypoxia and this was significantly reduced with rhEPO (p < 0.05). The neuronal marker, microtubule-associated protein-2, increased in expression (p < 0.05) when apoptosis was significantly reduced by rhEPO. In addition, compared with hypoxia alone, rhEPO-treated hypoxia had the following significant protein expression increases (p < 0.05): the intermediate filament structural protein nestin; myelin basic protein (oligodendrocytes); and glial fibrillary acidic protein (astrocytes). In conclusion, rhEPO protects the developing brain via anti-apoptotic mechanisms and promotes the health of non-neuronal as well as neuronal cell populations at a time when loss of these cells would have long-lasting effects on brain function.

Inaccurate measurement of free carnitine by the electrospray tandem mass spectrometry screening method for blood spots.

Abstract: An increasing number of laboratories screen for inherited metabolic diseases by electrospray tandem mass spectrometric analysis of extracts of blood spots from newborns (Chace et al 1995 ; Rashed et al 1995). The dried methanol extract of the blood spot, to which deuterium-labelled internal standards have been added, is butylated and infused into an electrospray tandem mass spectrometer. The concentrations of carnitine, acylcarnitines and amino acids are measured and compared with a normal reference range, and abnormal values are Ñagged. The standard butylation procedure involves heating the dried extract in 60 kl of anhydrous nbutanolÈ3 mol/L HCl at 65¡C for 15 min. Milder conditions a†ord incomplete butylation and the problems of interfering peaks and reduced sensitivity. Experiments in our laboratory have shown that (butylated) acylcarnitines are also converted to (butylated) carnitine in n-butanolÈ3 mol/L HCl. In separate experiments acetyl-, decanoylor octadecanoylcarnitine hydrochlorides (0.5 mmol/L) and hydrochloride (2.5 mmol/L) in n-butanolÈ3 mol/L HCl were heated L-(2H3)carnitine at 65¡C for 2 h. Five timed aliquots were removed, evaporated in a stream of nitrogen and dissolved in acetonitrileÈwaterÈformic acid (50 : 50 : 0.25). They were infused into the Ionspray of a PE Sciex API365 tandem mass spectrometer. The ratios of protonated molecular ions for butylated acylcarnitine to butylated Lwere measured from precursor ions scans of product ion m/z 85 and (2H3)carnitine plotted on a log scale against time for each acylcarnitine. From the straight-line decay graphs the half-life of each acylcarnitine in the butylating reagent was determined as well as the percentage butanolysed in 15 min. Acetylcarnitine has a half-life of 31 min and 30% butanolyses in 15 min ; decanoylcarnitine has a half-life of 125 min and 8% butanolyses in 15 min ; and octadecanoylcarnitine has a half-life of 172 min and 6% butanolyses in 15 min. Several implications derive from these observations. Some of the carnitine measured in the blood spot analysis comes from the acylcarnitines (including the deuterated internal standards). Consider a sample with low free carnitine and high acetylcarnitine. Thirty per cent of the acetylcarnitine as well as smaller amounts of higher molecular mass acylcarnitines are converted to carnitine and the lowcarnitine sample could appear to be normal. Prolonging the butylation time will not only result in a grossly inaccurate carnitine determination but will also reduce the signal intensity of the acylcarnitine ions during mass spectral analysis. Overnight butylation (15 h) will hydrolyse 97% of the high molecular mass acylcarnitines, i.e.

Standardized Outcomes in Nephrology-Peritoneal Dialysis (SONG-PD): Study Protocol for Establishing a Core Outcome Set in PD.

Abstract: BackgroundWorldwide, approximately 11% of patients on dialysis receive peritoneal dialysis (PD). Whilst PD may offer more autonomy to patients compared with hemodialysis, patient and caregiver burn...

Quality of life and alternate nightly nocturnal home hemodialysis

Abstract: Hemodialysis has been associated with reduced quality of life (QOL). Small cohort studies of quotidian hemodialysis regimens suggest general QOL and dialysis-related symptoms may improve compared with conventional regimens. An observational cohort study was conducted on 63 patients (age 51.7 +/- 12.9 years; 79.4% male; 33.3% diabetes; duration of renal replacement therapy 1.9 [0.7-6.4] years) converted from conventional home hemodialysis (3-5 sessions weekly, 3-6 h/session) to home nocturnal home hemodialysis (NHD) (3-5 sessions weekly, 6-10 h/session). Kidney Disease Quality of Life (KDQOL) and Assessment of Quality of Life instruments and 6-minute-walk tests were applied at baseline and 6 months. Baseline and 6 month surveys were returned by 70% of patients. On KDQOL, significant improvements in general health (P=0.02) and overall health ratings (P=0.0008), physical function (P=0.003), physical role (P=0.018), and energy and fatigue (P=0.027) were documented. There was a trend toward improvement in burden of kidney disease (P=0.05) and emotional role (P=0.066). There was a significant improvement in distance covered in the 6-minute-walk test from 513 m (420.5-576.4) to 536.5 m (459-609), P=0.007. On Assessment of Quality of Life, there was a trend toward improvement in overall utility score from 0.65 (0.39-0.81) to 0.73 (0.46-0.86), P=0.096. After 86.2 patient-years of observation, 23 patients have discontinued NHD (12 transplanted, 5 deceased, 4 psychosocial problems, 1 dialysis access problem, 1 medically unsuitable). Nocturnal home hemodialysis is a sustainable therapy. In addition to improving general QOL, alternate nightly NHD can significantly improve physical functioning as measured by KDQOL and 6-minute-walk tests.

Initial sequencing and analysis of the human genome.

Abstract: The human genome holds an extraordinary trove of information about human development, physiology, medicine and evolution. Here we report the results of an international collaboration to produce and make freely available a draft sequence of the human genome. We also present an initial analysis of the data, describing some of the insights that can be gleaned from the sequence.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

The social identity theory of intergroup behavior

Abstract: This chapter presents an outline of a theory of intergroup conflict and some preliminary data relating to the theory. Much of the work on the social psychology of intergroup relations has focused on patterns of individual prejudices and discrimination and on the motivational sequences of interpersonal interaction. The intensity of explicit intergroup conflicts of interests is closely related in human cultures to the degree of opprobrium attached to the notion of "renegade" or "traitor." The basic and highly reliable finding is that the trivial, ad hoc intergroup categorization leads to in-group favoritism and discrimination against the out-group. Many orthodox definitions of "social groups" are unduly restrictive when applied to the context of intergroup relations. The equation of social competition and intergroup conflict rests on the assumptions concerning an "ideal type" of social stratification in which the salient dimensions of intergroup differentiation are those involving scarce resources.