GAIP, GIPC and Galphai3 are concentrated in endocytic compartments of proximal tubule cells: putative role in regulating megalin's function

Megalin is the most abundant endocytic receptor in the proximal tubule epithelium (PTE), where it is concentrated in clathrin-coated pits (CCPs) and vesicles in the brush border region. The heterotrimeric G protein alpha subunit, Galphai3, has also been localized to the brush border region of PTE. By immunofluorescence GIPC and GAIP, components of G protein-mediated signaling pathways, are also concentrated in the brush border region of PTE and are present in megalin-expressing cell lines. By cell fractionation, these signaling molecules cosediment with megalin in brush border and microvillar fractions. GAIP is found by immunoelectron microscopy in CCPs, and GIPC is found in CCPs and apical tubules of endocytic compartments in the renal brush border. In precipitation assays, GST-GIPC specifically binds megalin. The concentration of Galphai3, GIPC, and GAIP with megalin in endocytic compartments of the proximal tubule, where extensive endocytosis occurs, and the interaction between GIPC and the cytoplasmic tail of megalin suggest a model whereby G protein-mediated signaling may regulate megalin's endocytic function and/or trafficking.     

Clinicians' attitudes to clinical practice guidelines: a systematic review

OBJECTIVE: To systematically review surveys of clinicians' attitudes to clinical practice guidelines. DATA SOURCES: MEDLINE, HealthStar, Embase and CINAHL were searched electronically for English-only surveys published from 1990 to 2000. STUDY SELECTION: We included surveys with responses to one or more of seven propositions (see below). Studies were excluded if they had fewer than 100 respondents or if the response rate was less than 60%. RESULTS: Thirty studies included responses to one or more of the seven items, giving a total of 11 611 responses. The response rate for the included studies was 72% (95% confidence interval [CI], 69%-75%). Clinicians agreed that guidelines were helpful sources of advice (weighted mean, 75%; 66%-83%), good educational tools (71%; 63%-79%) and intended to improve quality (70%; 60%-80%). However, clinicians also considered guidelines impractical and too rigid to apply to individual patients (30%; 23%-36%), that they reduced physician autonomy and oversimplified medicine (34%; 22%-47%), would increase litigation (41%; 32%-49%) and were intended to cut healthcare costs (52.8%; 39%-66%). CONCLUSIONS: Surveys of healthcare providers consistently report high satisfaction with clinical practice guidelines and a belief that they will improve quality, but there are concerns about the practicality of guidelines, their role in cost-cutting and their potential for increasing litigation.     

A birth-season/DRD4 gene interaction predicts weight gain and obesity in women with seasonal affective disorder: A seasonal thrifty phenotype hypothesis.

We have recently described an association between the hypofunctional 7-repeat allele (7R) of the dopamine-4 receptor gene (DRD4), weight gain, and obesity in women with seasonal affective disorder (SAD). In the current study, we examined whether season-of-birth might interact with the 7R allele to influence body weight regulation in SAD. In 182 female probands with SAD, we performed an analysis of covariance predicting maximum lifetime body mass index (BMI) with both the exon-3 variable number of tandem repeat polymorphism of DRD4 and season-of-birth as independent variables, and age as the covariate. The overall model was highly significant (F = 4.42, df = 8, 173, p < 0.0001) with season-of-birth predicting maximal lifetime BMI both on its own and in its interaction with the 7R allele. The latter finding was attributable to 7-repeat carriers born in the spring (N = 17), who had a mean maximal lifetime BMI of 33.7 kg/m2 (SD 8.6), compared to 26.7 kg/m2 (SD 5.4) for all other probands combined (N = 165) (F = 20.01, df = 1, 179, p < 0.0001). The lifetime rate of obesity (maximal BMI > 30 kg/m2) was also significantly higher in the 7R/spring birth group (9/17=52.9% vs 32/165=19.4%; chi2 = 9.94, df = 1, p = 0.002; odds ratio = 4.68, 95% CI = 1.67-13.07). These data may reflect a novel gene-environment interaction, during early brain development, which establishes an increased risk for obesity in women with SAD. Although the mechanism for season-of-birth effects in psychiatric disorders is unknown, a characteristic pattern of melatonin exposure during the second and third trimesters may be of particular relevance in this study population. We speculate that these data may reflect the vestigial expression of a seasonal thrifty phenotype that contributed to the positive selection of the 7R allele over the past 40,000 years.     

Pharmacokinetics of cyclosporin in children with stable renal transplants

Fourteen children, aged between 5 and 17 years, with stable renal graft function and stable cyclosporin A (CSA) trough levels (Cmin) were studied. They had been taking CSA 12-hourly since their transplant 1.5–9 years previously, with the average dose of Neoral being 6.4 (range 4.4–8.4) mg/kg per day. CSA whole blood levels were measured at 0, 20, and 40 min, and at 1, 1.5, 2, 2.5, 3, 4, 6, and 8 h following the morning dose using the Abbott TDx fluorescence polarization immunoassay. The area under the concentration time curve (AUC), clearance adjusted for bioavailability (CL/F), and steady-state volume of distribution adjusted for bioavailability (Vss/F) were determined using model-independent pharmacokinetic analysis. Delay time (Tdel), peak concentration (Cmax), time to peak concentration (Tmax), and Cmin were also determined and correlated with AUC and other parameters. The Tdel in absorption varied from 0.3 to 1.6 (mean 0.73) h, resulting in a similarly variable time to Tmax of 1–2.4 h (mean 1.59). Tmax was related to the age of the patient (Tmax=0.027age+1.41, r ²=0.56, P<0.005). The AUC showed good correlation with Cmax (Cmax=0.25AUC+423.32, r ²=0.96, P<0.0005). Cmax appears to be a more-suitable measure of exposure to CSA than Cmin. Prediction of Tmax from the age of the child may help to overcome the problem of when to collect blood for peak levels. Received: 23 July 1998 / Revised: 4 February 2000 / Accepted: 9 February 2000     

Superior therapeutic profile of poly-L-glutamic acid-paclitaxel copolymer compared with taxol in xenogeneic compartmental models of human ovarian carcinoma.

Previous preclinical studies with ectopic tumor models have demonstrated remarkable improvements in the therapeutic profile of paclitaxel, formulated as a copolymer with poly-L-glutamic acid, compared with paclitaxel in the clinical formulation, Taxol. In this study, we evaluated these formulations in two human ovarian carcinoma xenograft models, NMP-1 and HEY, in nude mice. i.p. implantation in female nude mice of either cell line gave rise to progressive disease within the peritoneum, in the parenchyma of visceral organs, and eventually at extraperitoneal sites; the resultant, increasing morbidity then required host sacrifice. i.p. administration of multiple-dose Taxol at its maximum tolerated dose 1 week after tumor implantation afforded minimal or no increased survival compared with controls in either model. Consistent with the predictions of drug copolymer behavior, paclitaxel, as the poly-L-glutamic acid-paclitaxel copolymer, displayed much less toxicity than Taxol in these hosts. When evaluated for antitumor efficacy in both the Taxol-resistant NMP-1 and HEY models, significant improvement in survival, and even some cures, were observed after a single i.p. treatment with this copolymer. The observed antitumor response correlated with histopathological analysis of peritoneal and extraperitoneal tumor burden in comparing control HEY mice sacrificed near the onset of morbidity with mice receiving paclitaxel copolymer. We conclude that both the i.p. NMP-1 and HEY models have significant value in establishing the efficacy of candidate agents, which might address Taxol-resistant human ovarian carcinoma. Furthermore, the poly-L-glutamic acid-paclitaxel copolymer has a superior therapeutic profile in these Taxol-resistant compartmental models.     

Pharmacokinetics and metabolism of the nitrogen mustard bioreductive drug 5-[N,N-bis(2-chloroethyl)amino]-2,4-dinitrobenzamide (SN 23862) and the corresponding aziridine (CB 1954) in KHT tumour-bearing mice

Purpose: To characterise the pharmacokinetics and metabolism in mice of 5-[N,N-bis(2-chloroethyl)amino]-2,4-dinitrobenzamide (SN 23862), the lead compound of a new class of bioreductive drugs in which a nitrogen mustard is activated by nitroreduction. Comparison is made with the corresponding aziridine derivative CB 1954. Methods: Male C₃H/HeN mice, bearing s.c. KHT tumours, received ³H-labelled SN 23862 or CB 1954 i.v. at 200 μmol/kg. Plasma, urine and tumour samples were assayed for total radioactivity, and for parent compounds by HPLC. Metabolites were identified by ¹H-NMR and mass spectrometry. Cytotoxicity of compounds against Chinese hamster AA8 cells was determined by growth inhibition assay. Results: The plasma pharmacokinetics of SN 23862 and CB 1954 were similar, with half-lives of 1.1 and 1.2 h, respectively. SN 23862 provided tumour/plasma ratios and absolute tumour AUC values almost two times higher than CB 1954. Despite this, SN 23862 was more extensively metabolised than CB 1954, the major route being sequential oxidative dechloroethylation of the nitrogen mustard moiety to the relatively non-toxic half mustard and 5-amine. The inferred chloroacetaldehyde co-product was 260 times more potent than SN 23862. A tetrahydroquinoxaline metabolite resulting from reduction of the 4-nitro group followed by intramolecular alkylation was weakly cytotoxic, while the more cytotoxic 2-amino derivative of SN 23862 was detected in trace amounts. CB 1954 was metabolised by analogous pathways, but the 4- and 2-amine nitroreduction products were the major metabolites while oxidative dealkylation was minor. Conclusion: The lesser propensity for SN 23862 to undergo nitroreduction in the host, relative to CB 1954, argues that dinitrobenzamide mustards may be preferable to the corresponding aziridines as bioreductive prodrugs for cancer treatment. However, the toxicological significance of oxidative metabolism of the bis(2-chloroethyl)amine moiety needs to be addressed. Received: 7 March 2000 / Accepted: 9 June 2000     

Psoas abscess — Fact and mimicry

Seven patients with processes involving the psoas muscle are presented. These included psoas abscess (3), metastatic tumor and abscess (1), lymphoma (1), and psoas hematoma (2). The role of radiologic studies in the diagnosis and management of these patients is discussed with particular reference to ultrasound and computed tomography.