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M J Field

Publications and source records attributed to M J Field.

At least 37 records · Page 2Linked to original sources
PubMed1999

Tertiary and quaternary conformational changes in aspartate transcarbamylase: a normal mode study.

Aspartate transcarbamylase (ATCase) initiates the pyrimidine biosynthetic pathway in Escherichia coli. Binding of aspartate to this allosteric enzyme induces a cooperative transition between the tensed (T) and relaxed (R) states of the enzyme which involves large quaternary and tertiary rearrangements. The mechanisms of the transmission of the regulatory signal to the active site (60 A away) and that of the cooperative transition are not known in detail, although a large number of single, double, and triple site-specific mutants and chimeric forms of ATCase have been obtained and kinetically characterized. A previous analysis of the very low-frequency normal modes of both the T and R state structures of ATCase identified some of the large-amplitude motions mediating the intertrimer elongation and rotation that occur during the cooperative transition (Thomas et al., J. Mol. Biol. 257:1070-1087, 1996; Thomas et al., J. Mol. Biol. 261:490-506, 1996). As a complement to that study, the deformation of the quaternary and tertiary structure of ATCase by normal modes below 5 cm(-1) is investigated in this article. The ability of the modes to reproduce the domain motions occurring during the transition is analyzed, with special attention to the interdomain closure in the catalytic chain, which has been shown to be critical for homotropic cooperativity. The calculations show a coupling between the quaternary motions and more localized motions involving specific residues. The particular dynamic behavior of these residues is examined in the light of biochemical results to obtain insights into their role in the transmission of the allosteric signal.

Allosteric Site↗
PubMed1999

Enadoline, a selective kappa-opioid receptor agonist shows potent antihyperalgesic and antiallodynic actions in a rat model of surgical pain.

Enadoline is a highly selective and potent kappa-opioid receptor agonist. This report describes and compares the activities of enadoline and morphine in a rat model of postoperative pain. A 1 cm incision through the muscle and skin of the plantar surface of the right hind paw induced thermal hyperalgesia as well as static and dynamic allodynia lasting at least 2 days. Postoperative testing was carried out using the plantar test for thermal hyperalgesia, von Frey hairs for static allodynia and light stroking with a cotton bud for dynamic allodynia. A single i.v. dose of enadoline 15 min before surgery dose-dependently (1-100 microg/kg) blocked the development of thermal hyperalgesia as well as static and dynamic allodynia for over 24 h with respective MEDs of < or = 1, 10 and 10 microg/kg. The administration of enadoline (100 microg/kg, i.v.), 1 h after surgery, completely blocked the maintenance of the hyperalgesic and allodynic responses, but its duration of action was much shorter (2 h) than when administered before surgery. Previous studies have shown that administration of morphine (1-6 mg/kg, s.c.) 0.5 h before surgery can prevent the development of thermal hyperalgesia with a MED of < or =1 mg/kg, but it has little effect on static allodynia. In the present study similar administration of morphine (1-3 mg/kg), unlike enadoline, had no effect on the development of dynamic allodynia. Morphine dose-dependently (1-6 mg/kg, s.c.) potentiated isoflurane-induced sleeping time and respiratory depression in the rat. However, whilst enadoline also (1-1000 microg/kg, i.v.) potentiated isoflurane-induced sleeping time, it did not cause respiratory depression. It is suggested that enadoline may possess therapeutic potential as a pre-emptive antihyperalgesic and antiallodynic agent.

Anesthesia Recovery Period↗
PubMed1999

Gabapentin and pregabalin, but not morphine and amitriptyline, block both static and dynamic components of mechanical allodynia induced by streptozocin in the rat.

A single injection of streptozocin (50 mg/kg, i.p.) led to the development of static and dynamic allodynia in the rat. The two responses were detected, respectively, by application of pressure using von Frey hairs or lightly stroking the hind paw with a cotton bud. Static allodynia was present in the majority of the animals within 10 days following streptozocin. In contrast, dynamic allodynia took almost twice as long to develop and was only present in approximately 60% of rats. Morphine (1-3 mg/kg, s.c.) and amitriptyline (0.25-2.0 mg/kg, p.o.) dose-dependently blocked static allodynia. However, neither of the compounds was effective against dynamic allodynia. In contrast, gabapentin (10-100 mg/kg, p.o.) and the related compound pregabalin (3-30 mg/kg, p.o.) dose-dependently blocked both types of allodynia. However, the corresponding R-enantiomer (10-100 mg/kg, p.o.) of pregabalin, was found to be inactive. The intrathecal administration of gabapentin dose-dependently (1-100 microg/animal) blocked both static and dynamic allodynia. In contrast, administration of similar doses of gabapentin into the hind paw failed to block these responses. It is suggested that in this model of neuropathic pain dynamic allodynia is mediated by A beta-fibres and the static type involves small diameter nociceptive fibres. These data suggest that gabapentin and pregabalin possess a superior antiallodynic profile than morphine and amitriptyline, and may represent a novel class of therapeutic agents for the treatment of neuropathic pain.

Acetates↗
PubMed1999

Detection of static and dynamic components of mechanical allodynia in rat models of neuropathic pain: are they signalled by distinct primary sensory neurones?

In the present study, chronic constrictive injury (CCI model) of the sciatic nerve or tight ligation of L5 and L6 spinal nerves (Chung model) produced both dynamic and static components of mechanical allodynia in rats. The two responses were detected, respectively, by lightly stroking the hind paw with cotton wool or application of pressure using von Frey hairs. Animals with spinal nerve ligation developed both types of responses at a faster rate compared to animals with the CCI. Morphine (1-3 mg/kg, s.c.) dose-dependently blocked static but not dynamic allodynia. In contrast, pregabalin (previously S-isobutylgaba and CI-1008) dose-dependently (3-30 mg/kg, p.o.) blocked both types of allodynia. In CCI animals, two administrations of capsaicin (100 microg/50 microl) into the plantar surface of the ipsilateral paw at 1-h intervals blocked the maintenance of thermal hyperalgesia without affecting either static or dynamic allodynia. The similar administration of a further two doses of capsaicin into the same animals blocked the maintenance of static allodynia without affecting the dynamic response. These data indicate that thermal hyperalgesia, static and dynamic allodynia are respectively signalled by C-, Adelta- and Abeta/capsaicin insensitive Adelta- primary sensory neurones. It is suggested that pregabalin possesses a superior antiallodynic profile than morphine and may represent a novel class of therapeutic agents for the treatment of neuropathic pain.

Animals↗
PubMed1999

Research agenda for developing measures to examine quality of care and quality of life of patients diagnosed with life-limiting illness.

Despite the universality of dying, research has not focused on developing conceptual models and measurement tools for examining the quality of care and quality of life of dying patients and their loved ones. We present here a vision and research agenda for the development of a Tool Kit of Instruments to Measure End of Life Care (TIME). Instruments for inclusion in the eventual "Tool Kit" should be patient-focused and family-centered, clinically meaningful, administratively manageable, and psychometrically sound. Prioritizing domains to measure quality of care should be based on consumer input and synergistic with ongoing efforts to formulate guidelines and standards of care. For this vulnerable population, research is needed regarding the timing and sources of data collection. In order to achieve maximal benefit, ultimately measurement tools must be incorporated into existing measurement systems and consideration be given to generating informative reports which leads to institutional action to improve the quality of care.

Humans↗
PubMed1999

Simulations of the T <--> R conformational transition in aspartate transcarbamylase.

Aspartate transcarbamylase (ATCase) from Escherichia coli is one of the best known allosteric enzymes. In spite of numerous experiments performed by biochemists, no consensus model for the cooperative transition between the tensed (T) and the relaxed (R) forms exists. It is hypothesized, however, that changes in the quaternary structure play a key role in the allosteric properties of oligomeric proteins such as ATCase. Previous normal mode calculations of the two states of ATCase illustrated the type of motions that could be important in initiating the transition. In this work four pathways for the transition were calculated using the targeted molecular dynamics (TMD) method without constraint on the symmetry of the system. The most important quaternary structure changes are the relative rotation and translation of the catalytic trimers and the rotations of the regulatory dimers. The simulations show that these quaternary changes start immediately and finish when about 70% of the transition is completed whereas there are tertiary changes throughout the transition. In agreement with the work of Lipscomb et al., it was found that the relative translation between the catalytic trimers appears to play a central role in allowing the transition to occur. In all the simulations differences are observed in the opening and closing behaviours of the domains in the catalytic and regulatory chains that could provide a structural interpretation for the results of certain site-directed mutagenesis experiments. Overall the motions of the subunits are concerted even though the constraint imposed on the TMD method does not explicitly require that this be so.

Aspartate Carbamoyltransferase↗
PubMed1999

In vitro effects of simvastatin on tubulointerstitial cells in a human model of cyclosporin nephrotoxicity.

To investigate the possibility that 3-hydroxy-3-methylglutaryl CoA (HMGCoA) reductase inhibitors ameliorate renal disease via direct effects on the tubulointerstitium, primary cultures of human proximal tubule cells (PTC) and renal cortical fibroblasts (CF) were exposed for 24 h to simvastatin (0.1-10 micromol/l) under basal conditions and in the presence of 1,000 ng/ml of cyclosporin (CsA), which we have previously shown to promote in vitro interstitial matrix accumulation at least partially via activation of local cytokine networks. Simvastatin, in micromolar concentrations, engendered cholesterol-independent inhibition of CF and PTC thymidine incorporation and cholesterol-dependent suppression of PTC apical Na+/H+ exchange (NHE) (ethylisopropylamiloride-sensitive apical 22Na+ uptake). Similarly, CF secretion of insulin-like growth factor-I (IGF-I) and IGF binding protein-3 were depressed, whereas CF collagen synthesis ([3H]proline incorporation) and PTC secretion of the fibrogenic cytokines, transforming growth factor-beta1, and platelet-derived growth factor were unaffected. A lower concentration (0.1 micromol/l) of simvastatin did not affect any of the above parameters under basal conditions but completely prevented CsA-stimulated CF collagen synthesis (control, 6.6 +/- 0.6; CsA, 8.3 +/- 0.6; CsA+simvastatin, 6.2 +/- 0.5%; P < 0.05) and IGF-I secretion (89.5 +/- 16.6, 204.7 +/- 57.0, and 94.6 +/- 22.3 ng. mg protein-1. day-1, respectively; P < 0.05). The results suggest that simvastatin exerts direct cholesterol-dependent and -independent effects on the human kidney tubulointerstitium. HMGCoA reductase inhibitors may ameliorate interstitial fibrosis complicating CsA therapy via direct actions on human renal cortical fibroblasts.

Aged↗
PubMed1999

Cyclosporin exerts a direct fibrogenic effect on human tubulointerstitial cells: roles of insulin-like growth factor I, transforming growth factor beta1, and platelet-derived growth factor.

To assess the direct fibrogenic effects of cyclosporin A (CyA) on the human tubulointerstitium, primary cultures of human renal proximal tubule cells (PTC) and renal cortical fibroblasts (CF) were incubated for 24 h with various concentrations of CyA. Cytotoxicity was confirmed in both cell populations by dose-dependent inhibition of thymidine incorporation, viability, and PTC apical sodium-hydrogen exchange activity (ethylisopropylamiloride-sensitive apical 22Na+ uptake). Compared with controls, both 500 and 1000 ng/ml CyA significantly stimulated CF collagen synthesis (proline incorporation 4.6 +/- 0.4, 6.5 +/- 0.8, and 7.1 +/- 1.0%, respectively; p <.05) and inhibited matrix metalloproteinase-2 (100%, 85.7 +/- 10.0%, and 38.8 +/- 9.2%) and matrix metalloproteinase-9 activity (100%, 110.6 +/- 19.0%, and 49.9 +/- 12.8%). CyA did not affect CF secretion of transforming growth factor beta1, but markedly stimulated insulin-like growth factor-I (IGF-I) secretion and inhibited secretion of both IGF-I binding protein-(IGFBP)-3 and IGFBP-2. CyA-induced CF collagen synthesis was abrogated by 5 microgram/ml anti-IGF-I receptor antibody, but not by 5 microgram/ml murine nonimmune globulin. Increasing concentrations of CyA progressively augmented PTC secretion of the fibrogenic cytokines transforming growth factor-beta1 and platelet-derived growth factor. These results indicate that clinically relevant concentrations of CyA are directly toxic to PTC and CF, irrespective of hemodynamic effects, and promote interstitial fibrosis by inhibiting matrix degradation and stimulating cortical fibroblast collagen synthesis via induction of autocrine IGF-I action. The latter effect may be further accentuated by the ability of CyA to augment secretion of transforming growth factor beta1 and platelet-derived growth factor by PTCs.

Cell Survival↗
PubMed1998

Role of insulin-like growth factor binding proteins in human post-nephrectomy proximal tubule cells.

1. In order to determine the role of the insulin-like growth factor-I (IGF-I)/IGF binding protein (IGFBP) axis in the augmentation of tubule growth and function following reductions in nephron mass, primary cultures of human proximal tubule cells (PTCs) were generated from the histologically normal sections of ten surgically removed kidneys. 2. PTC hypertrophy (cellular protein content), DNA synthesis (thymidine incorporation) and apical sodium-hydrogen exchange (NHE) activity (ethylisopropylamiloride-sensitive apical 22Na+ uptake) were measured following 24 h incubation in media supplemented with 10 % pre- or post-nephrectomy sera obtained from these patients. The results were compared with the effects of pre- and post-operative control sera collected from seven patients undergoing retroperitoneal operations not involving removal of renal tissue. 3. Day 1 post-nephrectomy sera promoted a significant 73 % increase in apical NHE activity, which was accompanied by a significant increase in PTC binding of 125I-IGF-I (post- vs. pre-nephrectomy, 163 +/- 6 vs. 142 +/- 4 fmol (mg protein)-1; P < 0.05). Subsequent post-nephrectomy sera significantly stimulated PTC protein content and thymidine incorporation, peaking at day 7 (127.7 +/- 14.0 and 118.4 +/- 9.0 % of pre-nephrectomy values, respectively; P < 0.05). The growth effects were cell specific, as they were not observed with renal cortical fibroblasts. No change was detected in any of these measured variables following exposure to control sera. 4. Serum IGF-I and IGFBP-1 levels did not significantly change over time or between groups. IGFBP-3 levels progressively decreased in both control and nephrectomized sera from pre-operative values of 3580 +/- 305 and 3360 +/- 217 ng ml-1, respectively, to 2670 +/- 341 and 2600 +/- 347 ng ml-1 at 1 week post-operation. Serum IGFBP-2 levels increased to a comparable extent in both controls (day 0 vs. day 7, 2940 +/- 1024 vs. 7010 +/- 2520 ng ml-1; P < 0.01) and nephrectomized patients (day 0 vs. day 7, 3070 +/- 656 vs. 9130 +/- 2010 ng ml-1; P < 0.01). 5. The results indicate that nephrectomy engenders the elaboration of one or more humoral factor(s), which promotes increased binding of IGF-I to PTCs and which may in turn specifically stimulate PTC Na+ transport and growth.

Cell Size↗
PubMed1998

Evaluation of PD 154075, a tachykinin NK1 receptor antagonist, in a rat model of postoperative pain.

PD 154075 ([(2-benzofuran)-CH2OCO]-(R)-alpha-MeTrp-(S)-NHCH(CH3) Ph) is a selective tachykinin NK1 receptor antagonist. Its effect on development and maintenance of thermal and mechanical hypersensitivity was examined in a rat model of surgical pain. When administered 30 min before surgery, PD 154075 dose-dependently (3-100 mg/kg, s.c.) prevented the development of thermal and mechanical hypersensitivity with respective minimum effective doses of 10 and 30 mg/kg. These antihypersensitivity effects lasted for 72 h. In contrast, the administration of PD 154075 (30 mg/kg, s.c.) after surgery had little or no effect on these nociceptive responses. PD 154075 antagonised thermal hypersensitivity induced by intrathecal administration of substance P, over the same dose range that blocked surgical hypersensitivity. However, it only partially blocked the thermal hypersensitivity induced by the selective NK2 receptor agonist [betaAla8]neurokinin A-(4-10). Morphine dose-dependently (1-6 mg/kg, s.c.) lengthened isoflurane and pentobarbitone-induced sleeping time in the rat. In contrast, PD 154075 (3-100 mg/kg, s.c.) did not interact with these anaesthetics. It is suggested that tachykinin NK1 receptor antagonists, such as PD 154075, may possess therapeutic potential as pre-emptive antihypersensitive agents.

Anesthetics↗
PubMed1998

Measuring quality of care at the end of life.

Caring for patients at the end of life presents a series of quality-of-care problems to the health care system. In the past, concern has focused on overaggressive treatment of dying patients. Given rapid changes in the financing and delivery of care, it is time to focus on a range of quality problems and address ways to improve care and achieve outcomes desired by patients and their families. We provide a framework for conceptualizing such a task. This article addresses the purposes of measurement, definition of the patient population, timing of measurement, use of surrogates in measurement, scope of services to be evaluated, and the choice of measures. It emphasizes the necessary links between quality measurement and quality improvement.

Continuity of Patient Care↗
PubMed1998

Second generation "peptoid" CCK-B receptor antagonists: identification and development of N-(adamantyloxycarbonyl)-alpha-methyl-(R)-tryptophan derivative (CI-1015) with an improved pharmacokinetic profile.

We have previously described the design and development of CI-988, a peptoid analogue of CCK-4 with excellent binding affinity and selectivity for the CCK-B receptor. Due to its anxiolytic profile in animal models of anxiety, this compound was developed as a clinical candidate. However, during its development, it was determined that CI-988 had low bioavailability in both rodent and nonrodent species. In the clinic, it was further established that CI-988 had poor bioavailability. Thus, there was a need to identify an analogue with an improved pharmacokinetic (PK) profile. The poor bioavailability was attributed to poor absorption and efficient hepatic extraction. We envisaged that reducing the molecular weight of the parent compound (5, MW = 614) would lead to better absorption. Thus, we synthesized a series of analogues in which the key alpha-methyltryptophan and adamantyloxycarbonyl moieties, required for receptor binding, were kept intact and the C-terminus was extensively modified. This SAR study led to the identification of tricyclo[3.3.1.1(3,7)]dec-2-yl [1S-[1 alpha(S*)2 beta]-[2-[(2-hydroxycyclohexyl)amino]-1-(1H-indol-3- ylmethyl)-1-methyl-2-oxoethyl]carbamate (CI-1015, 31) with binding affinities of 3.0 and 2900 nM for the CCK-B and CCK-A receptors, respectively. The compound showed CCK-B antagonist profile in the rat ventromedial hypothalamus assay with a Ke of 34 nM. It also showed an anxiolytic like profile orally in a standard anxiety paradigm (X-maze) with a minimum effective dose (MED) of 0.1 microgram/kg. Although the compound is less water soluble than CI-988, oral bioavailability in rat was improved nearly 10 times relative to CI-988 when dosed in HP beta CD. The blood-brain permeability of CI-1015 (31) was also enhanced relative to CI-988 (5). On the basis of the overall improved pharmacokinetic profile as well as enhanced brain penetration, CI-1015 (31) was chosen as a development candidate.

Adamantane↗
PubMed1998

Physiological changes in extracellular sodium directly control human proximal tubule growth and transport.

In order to examine the nature and potential mechanisms of action of extracellular sodium on human proximal tubule growth and transport, quiescent primary cultures of human proximal tubule cells (PTC) were incubated for 24 h in serum-free, growth-factor-free culture media containing low (130 mmol/l), control (140 mmol/l) or high (150 mmol/l) Na+. Compared to control conditions, cells exposed to a high Na+ concentration demonstrated stimulated thymidine incorporation (121.8 +/- 7.6%, P < 0.05) and increased cellular protein content (139.7 +/- 9.9%, P < 0.05); the latter arising from suppressed protein degradation ([3H]valine release 72.3 +/- 2.5%, P < 0.01) and unchanged protein synthesis ([3H]valine incorporation 98.5 +/- 2.6%, P > 0.1). Substitution of choline chloride for NaCl did not replicate these effects. Conversely, cells incubated in low-Na+ media showed reduced thymidine incorporation (77.2 +/- 4.4%, P < 0. 05), reduced protein synthesis (60.6 +/- 4.3%, P < 0.01), reduced protein degradation (79.5 +/- 1.8%, P < 0.01) and an unaltered protein content (102.4 +/- 8.8%). A role for apical Na+/H+ exchange (NHE) activity in mediating Na+-dependent alterations in PTC growth was suggested by the findings of increased apical, ethylisopropylamiloride- (EIPA)-sensitive 22Na+ uptake in the presence of a high Na+ concentration (159 +/- 19% of control, P < 0. 05) and concentration-dependent inhibition of cellular growth by EIPA at levels corresponding to those producing inhibition of apical NHE. Conditioned media from low Na+, control or high Na+ PTC contained comparable amounts of platelet-derived growth factor-AB (1. 19 +/- 0.23, 1.14 +/- 0.22 and 1.28 +/- 0.20 ng/mg protein, P > 0.1) and transforming growth factor-beta1 (1.76 +/- 0.32, 1.73 +/- 0.33 and 1.45 +/- 0.28 ng/mg protein, P > 0.1), and did not exhibit autocrine growth factor activity on separate PTC following adjustment of Na+ concentrations to 140 mmol/l by dialysis. Similarly, low-Na+, control or high-Na+ media did not modify the mitogenic responsiveness of PTC to insulin-like growth factor-I (IGF-I) or alter the affinity or number of PTC IGF-I binding sites. The results confirm that physiological increases in extracellular Na+ concentration directly stimulate human proximal tubule growth and Na+ transport. Such stimulation does not appear to be mediated by altered PTC secretion of, or responsiveness to, cytokines known to affect tubule growth and transport.

Aged↗
PubMed1998

Computer-based management of content in planning a problem-based medical curriculum.

The Faculty of Medicine at the University of Sydney has undertaken a major educational change from a traditional didactic 6-year, undergraduate entry programme to a 4-year problem-based programme to which only graduates are admitted. We have used two computer-based tools which proved invaluable in developing and managing the content of the new curriculum. The first, developed using a commercial database and made available on the Faculty's Intranet, provided a means for eliciting appropriate problems, organizing content fields and searching the information. The second, based on a spreadsheet, provided a means of displaying agreed content on implementation grids, both for self-directed learning and conventional teaching sessions. Both provided ready access for scrutiny, interactions, review and planning by staff and they greatly enhanced the process of understanding the nature of the new curriculum, and thus in reassuring staff about the change. By merging the two tools, a definitive curriculum database is emerging.

Decision Making, Computer-Assisted↗
PubMed1998

Paracrine stimulation of human renal fibroblasts by proximal tubule cells.

UNLABELLED: Paracrine stimulation of human renal fibroblasts by proximal tubule cells. BACKGROUND: Interstitial fibrosis strongly predicts the degree and progression of renal failure in human renal disorders. Since active fibrosis tends to initially occur in a peritubular distribution, the possibility that human proximal tubule cells (PTC) relay fibrogenic signals to neighboring cortical fibroblasts was examined in vitro. METHODS: Cell proliferation (cell counts and thymidine incorporation), total collagen synthesis (proline incorporation), matrix metalloproteinase (MMP) activity (gelatin zymography), and autocrine secretion of insulin-like growth factor-I (IGF-I) were measured in primary cultures of human cortical fibroblasts cocultured with PTC or exposed to PTC-conditioned media (PTCCM). RESULTS: Cell numbers and thymidine incorporation rates were increased in cortical fibroblasts cocultured with PTC (136.4+/-7.3% and 119.3+/-8.2% of control values, respectively, P < 0.05) or incubated in PTC-CM (114.0+/-5.9%, P < 0.05 and 146.7+/-13.3%, P < 0.05, respectively). PTC-CM stimulated cortical fibroblast collagen synthesis (13.5+/-1.0% vs. 10.8+/-0.7%, respectively, N = 24, P < 0.05) and MMP-2 and MMP-9 secretion. Cortical fibroblast secretion of IGF-I binding protein-3 (IGFBP-3), which in turn modulates the autocrine and paracrine actions of IGF-I, was enhanced in the presence of PTC-CM compared with control (1162.2+/-94.2 vs. 969.1+/-58.9 ng/mg protein/day, P < 0.05), but no change was observed in cortical fibroblast secretion of IGFBP-2 (260.9+/-38.8 vs. 290.9+/-36.6 ng/mg protein/day, P = NS) or IGF-I (56.7+/-6.6 vs. 57.0+/-6.8 ng/mg protein/day, P = NS). Human PTC secreted transforming growth factor-beta1 (TGF-beta1) and the AB heterodimer of platelet-derived growth factor (PDGF-AB) in a time-dependent fashion and the augmentation of cortical fibroblasts mitogenesis, collagen synthesis and IGFBP-3 secretion induced by PTC-CM was replicated by exogenous TGF-beta1 and PDGF. Furthermore, the stimulatory effects of PTC on cortical fibroblasts were potentiated in transiently acidified PTC-CM (which activated latent TGF-beta1), and were abrogated by neutralizing antibodies specifically directed against TGF-beta1 and PDGF-AB. Cortical fibroblasts in turn released a soluble factor(s) into cortical fibroblast-conditioned media that reciprocally stimulated PDGF-AB production by PTC (4.79+/-1.55 vs. 0.78+/-.06 ng/mg protein/day, P < 0.05). CONCLUSIONS: PTC modulate the biological behavior of neighboring cortical fibroblasts in the human kidney through paracrine mechanisms, which include the production and release of PDGF-AB and TGF-beta1. Renal insults that result in proximal tubule injury may perturb this paracrine interaction, thereby culminating in excessive fibroblast proliferation and interstitial fibrosis.

Adult↗
PubMed1998

TGF-beta 1 dissociates human proximal tubule cell growth and Na(+)-H+ exchange activity.

Stimulation of proximal tubule cell (PTC) growth in a variety of physiological and pathological renal conditions is preceded by increased renal production of transforming growth factor-beta 1 (TGF-beta 1) and by augmented tubular sodium transport via activated sodium hydrogen exchange (NHE). Since TGF-beta 1 has been shown to be an important paracrine and autocrine regulator of PTC growth, the hypothesis that TGF-beta 1 modulates basal and mitogen-stimulated PTC growth via an effect on NHE activity was examined. Confluent, quiescent, human PTC were incubated for 24 hours in serum-free media containing vehicle (control) or 1 ng/ml TGF-beta 1, in the presence or absence of 100 ng/ml insulin-like growth factor-1 (IGF-I). Under basal conditions, TGF-beta 1 inhibited thymidine incorporation (73.5 +/- 7.3% of control, P < 0.05), but exerted no effect on cellular protein content (97.4 +/- 10.7% of control), an index of hypertrophy. There was no significant alteration of NHE activity, measured as ethylisopropylamiloride (EIPA)-sensitive H+ efflux (2.72 +/- 0.50 vs. control 3.26 +/- 0.68 mmol/liter/min) or 22Na+ influx (2.20 +/- 0.23 vs. control 2.19 +/- 0.19 nmol/mg protein/min). When co-incubated with IGF-I. TGF-beta 1 induced significant PTC hypertrophy (116.9 +/- 8.2% of control, P < 0.05), which was not seen with either agent alone. TGF-beta 1 counteracted the stimulatory effect of IGF-I on DNA synthesis (TGF-beta 1 + IGF-I 103.0 +/- 7.3% vs. IGF-I alone 181.2 +/- 30.3% of control, P < 0.05), but did not affect IGF-I-stimulated EIPA-sensitive 22Na+ influx (3.63 +/- 0.63 vs. IGF-I alone 3.67 +/- 0.50 nmol/mg protein/min, P = NS, both vs. control 2.19 +/- 0.19 nmol/mg protein/min, P < 0.05). Similar results were obtained when NHE activity was measured as EIPA-sensitive H+ efflux. Moreover, the kinetics of NHE activation by the combination of TGF-beta 1 and IGF-I (involving an increase in Vmax) were identical to that previously found for PTC exposed to IGF-I alone. The study demonstrates that TGF-beta 1 elicits distinct PTC growth responses in the presence and absence of IGF-I, without modification of NHE activity. The combination of predominant PTC hypertrophy and enhanced proximal tubule Na+ reabsorption found in many conditions that are associated with renal growth is likely to require the integrated actions of both TGF-beta 1 and IGF-I.

Aged↗