Therapeutic resistance in acute myeloid leukemia cells is mediated by a novel ATM/mTOR pathway regulating oxidative phosphorylation

While leukemic cells are susceptible to various therapeutic insults, residence in the bone marrow microenvironment typically confers protection from a wide range of drugs. Thus, understanding the unique molecular changes elicited by the marrow is of critical importance towards improving therapeutic outcomes. In the present study, we demonstrate that aberrant activation of oxidative phosphorylation serves to induce therapeutic resistance in FLT3 mutant human AML cells challenged with FLT3 inhibitor drugs. Importantly, our findings show that AML cells are protected from apoptosis following FLT3 inhibition due to marrow-mediated activation of ATM, which in turn up-regulates oxidative phosphorylation via mTOR signaling. mTOR is required for the bone marrow stroma-dependent maintenance of protein translation, with selective polysome enrichment of oxidative phosphorylation transcripts, despite FLT3 inhibition. To investigate the therapeutic significance of this finding, we tested the mTOR inhibitor everolimus in combination with the FLT3 inhibitor quizartinib in primary human AML xenograft models. While marrow resident AML cells were highly resistant to quizartinib alone, the addition of everolimus induced profound reduction in tumor burden and prevented relapse. Taken together, these data provide a novel mechanistic understanding of marrow-based therapeutic resistance, and a promising strategy for improved treatment of FLT3 mutant AML patients.

Abstract 1442: Targeting ATM kinase and mTOR signaling reverses bone marrow stromal cell-mediated protection of FLT3-ITD AML from FLT3-targeted therapy

Internal tandem duplication (ITD) mutations in FMS-like tyrosine kinase 3 (FLT3) are among the most common mutations in acute myeloid leukemia (AML) and are associated with poor prognosis. FLT3-ITD causes constitutive activation of FLT3, and the strong evidence that activated FLT3 drives leukemogenesis has led to the development of several FLT3-targeted inhibitors. However, clinical studies of FLT3-targeted inhibitors have demonstrated much more effective clearing of leukemic burden in the periphery than in the bone marrow, implicating the bone marrow microenvironment as a potential contributor to drug resistance. As previously reported, the conditioned media of human bone marrow stromal cells (CM-BMSC) protects human FLT3-ITD AML cells from the killing effect of FLT3-targeted therapy despite complete inhibition of FLT3. We further show that genetic knockdown of Ataxia Telangiectasia Mutated (ATM) in combination with FLT3 inhibition substantially reverses the protection from cell death mediated by CM-BMSC. While autophosphorylation activity of ATM is downregulated upon FLT3 inhibition in regular media, CM-BMSC prevented the loss of ATM activity. Interestingly, genetic knockdown of ATM in human FLT3-ITD AML cells impaired the activity of mTOR Complex 1, and unbiased analyses of gene expression and signaling pathways by RNA-seq analysis and Reverse Phase Protein Arrays (RPPA) showed that mTOR signaling is downregulated with FLT3 inhibition in regular media, coinciding with marked inhibition of the protein translation machinery. Both mTOR signaling and protein translation were maintained during FLT3 inhibition in the presence of CM-BMSC. Furthermore, human FLT3-ITD AML cells treated with mTOR inhibitor everolimus in combination with the FLT3 inhibitor quizartinib reversed the protection mediated by CM-BMSC, and combination therapies are currently being tested in mouse models. These data suggest that ATM kinase and mTOR signaling play a key role in bone marrow stoma-mediated protection against FLT3 targeted therapy. Findings from this research provide new insights into the mechanism of bone marrow stroma-mediated protection of FLT3-ITD AML from FLT3-targeted therapy, identifying additional candidates for combinatorial therapies designed to overcome the protective effects of bone marrow stromal cells and improve patient outcomes.

Citation Format: Hae J. Park, Mark A. Gregory, Vadym Zaberezhnyy, James DeGregori. Targeting ATM kinase and mTOR signaling reverses bone marrow stromal cell-mediated protection of FLT3-ITD AML from FLT3-targeted therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1442.

Modifiable factors related to life-space mobility in community-dwelling older adults: results from the Canadian Longitudinal Study on Aging

BACKGROUND

The most common methods for measuring mobility in older adulthood include performance-based tests, such as the Timed-Up-and-Go and gait speed. While these measures have strong predictive validity for adverse outcomes, they are limited to assessing what older adults do in standardized settings, rather than what they do in their daily life. Life-space mobility, which is the ability to move within environments that expand from one's home to the greater community, has been proposed as a more comprehensive measure of mobility. The aim of this study was to determine the association between modifiable factors and life-space mobility in older adults enrolled in the Canadian Longitudinal Study on Aging (CLSA).

METHODS

Life-space mobility was measured using the Life Space Index (LSI). Explanatory factors included physical, psychosocial and cognitive determinants, as well as pain, fatigue, driving status, nutrition, body mass index, smoking status, and vision. To estimate the association between the LSI and explanatory variables, univariate and multivariable ordinary least squares regression analyses were performed.

RESULTS

All adults 65 years and older (n = 12,646) were included in the analysis. Fifty percent were women and the mean age was 73.0 (SD5.7). The mean LSI score was 80.5, indicating that, on average, the sample was able to move outside of their neighborhood independently. All explanatory variables were significantly associated with the LSI except for balance and memory. The top 3 variables that explained the most variation in the LSI were driving, social support and walking speed.

CONCLUSION

To our knowledge, this was the first study to examine the association between life-space mobility and a comprehensive set of modifiable factors that were selected based on a theoretical framework and existing research evidence. This study had two important messages. First, driving, social support and walking speed emerged as the most significant correlates of life-space mobility in older adults. Second, life-space mobility is multifactorial and interventions that are pragmatic in their design and testing are needed that consider the complexity involved. A multi-disciplinary approach to examining life-space mobility in older adults is needed to optimize opportunities for healthy aging and develop strategies that support mobility in older adulthood.

Targeting Glutamine Metabolism and Redox State for Leukemia Therapy

PURPOSE

Acute myeloid leukemia (AML) is a hematologic malignancy characterized by the accumulation of immature myeloid precursor cells. AML is poorly responsive to conventional chemotherapy and a diagnosis of AML is usually fatal. More effective and less toxic forms of therapy are desperately needed. AML cells are known to be highly dependent on the amino acid glutamine for their survival. These studies were directed at determining the effects of glutaminase inhibition on metabolism in AML and identifying general weaknesses that can be exploited therapeutically.

EXPERIMENTAL DESIGN

AML cancer cell lines, primary AML cells, and mouse models of AML and acute lymphoblastic leukemia (ALL) were utilized.

RESULTS

We show that blocking glutamine metabolism through the use of a glutaminase inhibitor (CB-839) significantly impairs antioxidant glutathione production in multiple types of AML, resulting in accretion of mitochondrial reactive oxygen species (mitoROS) and apoptotic cell death. Moreover, glutaminase inhibition makes AML cells susceptible to adjuvant drugs that further perturb mitochondrial redox state, such as arsenic trioxide (ATO) and homoharringtonine (HHT). Indeed, the combination of ATO or HHT with CB-839 exacerbates mitoROS and apoptosis, and leads to more complete cell death in AML cell lines, primary AML patient samples, and in vivo using mouse models of AML. In addition, these redox-targeted combination therapies are effective in eradicating ALL cells in vitro and in vivo.

CONCLUSIONS

Targeting glutamine metabolism in combination with drugs that perturb mitochondrial redox state represents an effective and potentially widely applicable therapeutic strategy for treating multiple types of leukemia.

The 4G to 5G Network Architecture Evolution in Australia

This paper provides a review of selected design and security aspects of 5G systems and addresses key questions about the deployment scenarios of Next Generation Radio Access Networks in Australia. The paper first presents the most relevant 5G use cases for the Australian market in 2018-19, and beyond; 5G concept and definitions; 3GPP updates, in terms of system architecture and enabling technologies and corresponding timelines; and spectrum availability, linked to possible 5G deployments in Australia. Then, the paper discusses the 5G functional architecture, possible configuration options, enabling technologies and network migration strategies and related 5G security, in Australia and globally. This is followed by a description of the possible 5G deployment scenarios in a multivendor environment and includes, as a case study, the Huawei product portfolio and site solution in Australia. The paper concludes with a discussion on the potential benefits of a telecommunications security assurance centre to improve the whole-of-life security assurance of critical telecommunications infrastructure and why it is important for the Australia telecommunications sector.

Distributed efficient similarity search mechanism in wireless sensor networks

The Wireless Sensor Network similarity search problem has received considerable research attention due to sensor hardware imprecision and environmental parameter variations. Most of the state-of-the-art distributed data centric storage (DCS) schemes lack optimization for similarity queries of events. In this paper, a DCS scheme with metric based similarity searching (DCSMSS) is proposed. DCSMSS takes motivation from vector distance index, called iDistance, in order to transform the issue of similarity searching into the problem of an interval search in one dimension. In addition, a sector based distance routing algorithm is used to efficiently route messages. Extensive simulation results reveal that DCSMSS is highly efficient and significantly outperforms previous approaches in processing similarity search queries.

Tyrosine kinase inhibition in leukemia induces an altered metabolic state sensitive to mitochondrial perturbations

PURPOSE

Although tyrosine kinase inhibitors (TKI) can be effective therapies for leukemia, they fail to fully eliminate leukemic cells and achieve durable remissions for many patients with advanced BCR-ABL(+) leukemias or acute myelogenous leukemia (AML). Through a large-scale synthetic lethal RNAi screen, we identified pyruvate dehydrogenase, the limiting enzyme for pyruvate entry into the mitochondrial tricarboxylic acid cycle, as critical for the survival of chronic myelogenous leukemia (CML) cells upon BCR-ABL inhibition. Here, we examined the role of mitochondrial metabolism in the survival of Ph(+) leukemia and AML upon TK inhibition.

EXPERIMENTAL DESIGN

Ph(+) cancer cell lines, AML cell lines, leukemia xenografts, cord blood, and patient samples were examined.

RESULTS

We showed that the mitochondrial ATP-synthase inhibitor oligomycin-A greatly sensitized leukemia cells to TKI in vitro. Surprisingly, oligomycin-A sensitized leukemia cells to BCR-ABL inhibition at concentrations of 100- to 1,000-fold below those required for inhibition of respiration. Oligomycin-A treatment rapidly led to mitochondrial membrane depolarization and reduced ATP levels, and promoted superoxide production and leukemia cell apoptosis when combined with TKI. Importantly, oligomycin-A enhanced elimination of BCR-ABL(+) leukemia cells by TKI in a mouse model and in primary blast crisis CML samples. Moreover, oligomycin-A also greatly potentiated the elimination of FLT3-dependent AML cells when combined with an FLT3 TKI, both in vitro and in vivo.

CONCLUSIONS

TKI therapy in leukemia cells creates a novel metabolic state that is highly sensitive to particular mitochondrial perturbations. Targeting mitochondrial metabolism as an adjuvant therapy could therefore improve therapeutic responses to TKI for patients with BCR-ABL(+) and FLT3(ITD) leukemias.

Inhibition of calcineurin combined with dasatinib has direct and indirect anti-leukemia effects against BCR-ABL1(+) leukemia

Treatment of BCR-ABL1(+) leukemia has been revolutionized with the development of tyrosine kinase inhibitors. However, patients with BCR-ABL1(+) acute lymphoblastic leukemia and subsets of patients with chronic myeloid leukemia are at high risk of relapse despite kinase inhibition therapy, necessitating novel treatment strategies. We previously reported synthetic lethality in BCR-ABL1(+) leukemia cells by blocking both calcineurin/NFAT signaling and BCR-ABL1, independent of drug efflux inhibition by cyclosporine. Here, using RNA-interference we confirm that calcineurin inhibition sensitizes BCR-ABL1(+) cells to tyrosine kinase inhibition in vitro. However, when we performed pharmacokinetic and pharmacodynamic studies of dasatinib and cyclosporine in mice, we found that co-administration of cyclosporine increases peak concentrations and the area under the curve of dasatinib, which contributes to the enhanced disease control. We also report the clinical experience of two subjects in whom we observed more hematopoietic toxicity than expected while enrolled in a Phase Ib trial designed to assess the safety and tolerability of adding cyclosporine to dasatinib in humans. Thus, the anti-leukemia benefit of co-administration of cyclosporine and dasatinib is mechanistically pleiotropic, but may not be tolerable, at least as administered in this trial. These data highlight some of the challenges associated with combining targeted agents to treat leukemia.

Rational combination of a MEK inhibitor, selumetinib, and the Wnt/calcium pathway modulator, cyclosporin A, in preclinical models of colorectal cancer

PURPOSE

The mitogen-activated protein kinase (MAPK) pathway is a crucial regulator of cell proliferation, survival, and resistance to apoptosis. MEK inhibitors are being explored as a treatment option for patients with KRAS-mutant colorectal cancer who are not candidates for EGFR-directed therapies. Initial clinical results of MEK inhibitors have yielded limited single-agent activity in colorectal cancer, indicating that rational combination strategies are needed.

EXPERIMENTAL DESIGN

In this study, we conducted unbiased gene set enrichment analysis and synthetic lethality screens with selumetinib, which identified the noncanonical Wnt/Ca++ signaling pathway as a potential mediator of resistance to the MEK1/2 inhibitor selumetinib. To test this, we used shRNA constructs against relevant WNT receptors and ligands resulting in increased responsiveness to selumetinib in colorectal cancer cell lines. Further, we evaluated the rational combination of selumetinib and WNT pathway modulators and showed synergistic antiproliferative effects in in vitro and in vivo models of colorectal cancer.

RESULTS

Importantly, this combination not only showed tumor growth inhibition but also tumor regression in the more clinically relevant patient-derived tumor explant (PDTX) models of colorectal cancer. In mechanistic studies, we observed a trend toward increased markers of apoptosis in response to the combination of MEK and WntCa(++) inhibitors, which may explain the observed synergistic antitumor effects.

CONCLUSIONS

These results strengthen the hypothesis that targeting both the MEK and Wnt pathways may be a clinically effective rational combination strategy for patients with metastatic colorectal cancer.

Thr 163 phosphorylation causes Mcl-1 stabilization when degradation is independent of the adjacent GSK3-targeted phosphodegron, promoting drug resistance in cancer

The antiapoptotic Bcl-2 family member Mcl-1 is a PEST protein (containing sequences enriched in proline, glutamic acid, serine, and threonine) and is subject to rapid degradation via multiple pathways. Impaired degradation leading to the maintenance of Mcl-1 expression is an important determinant of drug resistance in cancer. Phosphorylation at Thr 163 in the PEST region, stimulated by 12-O-tetradecanoylphorbol acetic acid (TPA)-induced activation of extracellular signal-regulated kinase (ERK), is associated with Mcl-1 stabilization in BL41-3 Burkitt lymphoma cells. This contrasts with the observation that Thr 163 phosphorylation in normal fibroblasts primes glycogen synthase kinase (GSK3)-induced phosphorylation at Ser 159, producing a phosphodegron that targets Mcl-1 for degradation. In the present follow-up studies in BL41-3 cells, Mcl-1 degradation was found to be independent of the GSK3-mediated pathway, providing a parallel to emerging findings showing that Mcl-1 degradation through this pathway is lost in many different types of cancer. Findings in Mcl-1-transfected CHO cells corroborated those in BL41-3 cells in that the GSK3-targeted phosphodegron did not play a major role in Mcl-1 degradation, and a phosphomimetic T163E mutation resulted in marked Mcl-1 stabilization. TPA-treated BL41-3 cells, in addition to exhibiting Thr 163 phosphorylation and Mcl-1 stabilization, exhibited an ∼10-fold increase in resistance to multiple chemotherapeutic agents, including Ara-C, etoposide, vinblastine, or cisplatin. In these cancer cells in which Mcl-1 degradation is not dependent on the GSK3/phosphodegron-targeted pathway, ERK activation and Thr 163 phosphorylation are associated with pronounced Mcl-1 stabilization and drug resistance – effects that can be suppressed by inhibition of ERK activation.

Abstract 3796: Inhibition of mitochondrial respiration synergizes with tyrosine kinase inhibitors to eliminate Bcr-Abl+ leukemia

Bcr-Abl kinase inhibitors are the standard therapy for chronic myelogenous leukemia (CML). While effective in controlling disease in chronic phase, these inhibitors often fail to completely eliminate Bcr-Abl+ CML cells and also fail to achieve durable remissions for advanced CML and Bcr-Abl+ acute lymphoblastic leukemias (ALL). Our lab employed a large-scale synthetic lethal shRNA screen to identify genes involved in CML survival upon treatment with the Bcr-Abl kinase inhibitor imatinib (IM) [Cancer Cell. 2010;18(1):74-87]. This screen identified several genes involved in energy utilization including a component of pyruvate dehydrogenase, dihydrolipoyllysine-residue acetyltransferase. This target was identified by two independent shRNAs, each underrepresented over 22 fold in treated cells compared to untreated. CML proliferation depends on Bcr-Abl-driven glycolysis for energy production. Upon IM treatment, I hypothesized that these cells are forced to rely on other sources of energy including the TCA cycle and mitochondrial respiration, and that targeting alternative energy production pathways will enhance IM-mediated elimination of CML cells. Thus, I predicted that inhibition of mitochondrial respiration by knockdown or pharmacologic inhibition would cooperate with tyrosine kinase inhibitors to eliminate Bcr-Abl+ leukemias. My experiments have shown that knocking down pyruvate dehydrogenase in human blast crisis Bcr-Abl+ CML cells (K562) greatly sensitizes cells to IM in vitro. Conversely, supplementing the cell culture media with increasing concentrations of methyl-pyruvate protects K562 cells from IM treatment. Moreover, I find that the mitochondrial ATP-synthase inhibitor Oligomycin A also synergizes with IM to kill CML cells in vitro. In addition, inhibition of mitochondrial respiration with Oligomycin A enhances elimination of Bcr-Abl+ cells by a Bcr-Abl tyrosine kinase inhibitor in vivo and prolongs disease-free survival in a mouse model of Bcr-Abl+ B-ALL. The drug doses of Oligomycin A used are over 100-fold below the LD50, and have no apparent adverse effects on these mice. Targeting mitochondrial metabolism as an adjuvant drug therapy may prevent the survival of residual Bcr-Abl+ CML cells upon tyrosine kinase inhibitor treatment.

*This project is supported in part by pre-doctoral fellowship number F31CA157166 from the National Cancer Institute.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3796. doi:10.1158/1538-7445.AM2011-3796

Wnt/Ca2+/NFAT signaling maintains survival of Ph+ leukemia cells upon inhibition of Bcr-Abl

Although Bcr-Abl kinase inhibitors have proven effective in the treatment of chronic myeloid leukemia (CML), they generally fail to eradicate Bcr-Abl(+) leukemia cells. To identify genes whose inhibition sensitizes Bcr-Abl(+) leukemias to killing by Bcr-Abl inhibitors, we performed an RNAi-based synthetic lethal screen with imatinib mesylate in CML cells. This screen identified numerous components of a Wnt/Ca(2+)/NFAT signaling pathway. Antagonism of this pathway led to impaired NFAT activity, decreased cytokine production, and enhanced sensitivity to Bcr-Abl inhibition. Furthermore, NFAT inhibition with cyclosporin A facilitated leukemia cell elimination by the Bcr-Abl inhibitor dasatinib and markedly improved survival in a mouse model of Bcr-Abl(+) acute lymphoblastic leukemia (ALL). Targeting this pathway in combination with Bcr-Abl inhibition could improve treatment of Bcr-Abl(+) leukemias.

Compressed air massage hastens healing of the diabetic foot

BACKGROUND

The management of diabetic foot ulcers remains a problem. A treatment modality that uses compressed air massage has been developed as a supplement to standard surgical and medical treatment. Compressed air massage is thought to improve local tissue oxygenation around ulcers. The aim of this study was to determine whether the addition of compressed air massage influences the rate of healing of diabetic ulcers.

METHODS

Sixty consecutive patients with diabetes, admitted to one hospital for urgent surgical management of diabetic foot ulcers, were randomized into two groups. Both groups received standard medical and surgical management of their diabetes and ulcer. In addition, one group received 15-20 min of compressed air massage, at 1 bar pressure, daily, for 5 days a week, to the foot and the tissue around the ulcer. Healing time was calculated as the time from admission to the time of re-epithelialization.

RESULTS

Fifty-seven patients completed the trial; 28 received compressed air massage. There was no difference in the mean age, Wagner score, ulcer size, pulse status, or peripheral sensation in the two groups. The time to healing in the compressed air massage group was significantly reduced: 58.1 +/- 22.3 days (95% confidence interval: 49.5-66.6) versus 82.7 +/- 30.7 days (95% confidence interval: 70.0-94.3) (P = 0.001). No adverse effects in response to compressed air massage were noted.

CONCLUSIONS

The addition of compressed air massage to standard medical and surgical management of diabetic ulcers appears to enhance ulcer healing. Further studies with this new treatment modality are warranted.

The ARF tumor suppressor: keeping Myc on a leash

The ARF tumor suppressor protein acts in a checkpoint that guards against unscheduled cellular proliferation in response to oncogenic signaling. Deregulated expression of c-Myc induces ARF expression and apoptosis through the ARF-Mdm2-p53 axis. Our recent study reveals a new direct role for ARF in controlling c-Myc's oncogenic activity that is independent of p53. ARF binds to and selectively impairs the transactivation ability of c-Myc while leaving its transrepression ability intact. Biologically, ARF prevents hyper-proliferation and transformation caused by c-Myc and enhances c-Myc-induced apoptosis independently of p53. These new findings may be especially relevant for therapeutic strategies targeting c-Myc-induced cancers.

p19ARF directly and differentially controls the functions of c-Myc independently of p53

Increased expression of the oncogenic transcription factor c-Myc causes unregulated cell cycle progression. c-Myc can also cause apoptosis, but it is not known whether the activation and/or repression of c-Myc target genes mediates these diverse functions of c-Myc. Because unchecked cell cycle progression leads to hyperproliferation and tumorigenesis, it is essential for tumour suppressors, such as p53 and p19ARF (ARF), to curb cell cycle progression in response to increased c-Myc (refs 2, 3). Increased c-Myc has previously been shown to induce ARF expression, which leads to cell cycle arrest or apoptosis through the activation of p53 (ref. 4). Here we show that ARF can inhibit c-Myc by a unique and direct mechanism that is independent of p53. When c-Myc increases, ARF binds with c-Myc and dramatically blocks c-Myc's ability to activate transcription and induce hyperproliferation and transformation. In contrast, c-Myc's ability to repress transcription is unaffected by ARF and c-Myc-mediated apoptosis is enhanced. These differential effects of ARF on c-Myc function suggest that separate molecular mechanisms mediate c-Myc-induced hyperproliferation and apoptosis. This direct feedback mechanism represents a p53-independent checkpoint to prevent c-Myc-mediated tumorigenesis.

MCL1 is phosphorylated in the PEST region and stabilized upon ERK activation in viable cells, and at additional sites with cytotoxic okadaic acid or taxol

BCL2 family members are subject to regulation at multiple levels, providing checks on their ability to contribute to tumorigenesis. However, findings on post-translational BCL2 phosphorylation in different systems have been difficult to integrate. Another antiapoptotic family member, MCL1, exhibits a difference in electrophoretic mobility upon phosphorylation induced by an activator of PKC (12-O-tetradecanoylphorbol 13-acetate; TPA) versus agents that act on microtubules or protein phosphatases 1/2A. A multiple pathway model is now presented, which demonstrates that MCL1 can undergo distinct phosphorylation events - mediated through separate signaling processes and involving different target sites - in cells that remain viable in the presence of TPA versus cells destined to die upon exposure to taxol or okadaic acid. Specifically, TPA induces phosphorylation at a conserved extracellular signal-regulated kinase (ERK) site in the PEST region (Thr 163) and slows turnover of the normally rapidly degraded MCL1 protein; however, okadaic acid and taxol induce ERK-independent MCL1 phosphorylation at additional discrete sites. These findings add a new dimension to our understanding of the complex regulation of antiapoptotic BCL2 family members by demonstrating that, in addition to transcriptional and post-transcriptional regulation, MCL1 is subject to multiple, separate, post-translational phosphorylation events, produced in living versus dying cells at ERK-inducible versus ERK-independent sites.

Phosphorylation by Glycogen Synthase Kinase-3 Controls c-Myc Proteolysis and Subnuclear Localization

The c-Myc protein is a transcription factor that is a central regulator of cell growth and proliferation. Thr-58 is a major phosphorylation site in c-Myc and is a mutational hotspot in Burkitt's and other aggressive human lymphomas, indicating that Thr-58 phosphorylation restricts the oncogenic potential of c-Myc. Mutation of Thr-58 is also associated with increased c-Myc protein stability. Here we show that inhibition of glycogen synthase kinase-3 (GSK-3) activity with lithium increases c-Myc stability and inhibits phosphorylation of c-Myc specifically at Thr-58 in vivo. Conversely, overexpression of GSK-3 alpha or GSK-3 beta enhances Thr-58 phosphorylation and ubiquitination of c-Myc. Together, these observations suggest that phosphorylation of Thr-58 mediated by GSK-3 facilitates c-Myc rapid proteolysis by the ubiquitin pathway. Furthermore, we demonstrate that GSK-3 binds c-Myc in vivo and in vitro and that GSK-3 colocalizes with c-Myc in the nucleus, strongly arguing that GSK-3 is the c-Myc Thr-58 kinase. We found that c-MycS, which lacks the N-terminal 100 amino acids of c-Myc, is unable to bind GSK-3; however, mutation of Ser-62, the priming phosphorylation site necessary for Thr-58 phosphorylation, does not disrupt GSK-3 binding. Finally, we show that Thr-58 phosphorylation alters the subnuclear localization of c-Myc, enhancing its localization to discrete nuclear bodies together with GSK-3.

Metal accumulation, filtration and O(2) uptake rates in the mussel Perna perna (Mollusca: Bivalvia) exposed to Hg(2+), Cu(2+) and Zn(2+)

Tissue metal concentrations, filtration and oxygen uptake rates were investigated for Perna perna (Bivalvia: Mollusca) during exposure to Hg(2+), Cu(2+) and Zn(2+) (50 microg/l for 24 days, and 24 days recovery with no metal). Hg and Cu tissue levels increased with exposure time, reaching maximum levels after 24 days (87.5 microg Hg/g dry mass and 45 microg Cu/g dry mass, respectively). Zn levels peaked after 4 days exposure (to 233 microg Zn/g dry mass) and stabilized thereafter. Accumulated metal was rapidly lost from tissues when mussels were returned to uncontaminated seawater, suggesting that tissue concentration data may be of limited use in biomonitoring situations where environmental metals fluctuate to low levels. Filtration rates fell below control rates during Hg(2+) exposure, and became elevated again during the recovery period. Cu(2+) and Zn(2+) exposure had little effect on filtration, but suppressed oxygen uptake. During recovery, oxygen uptake of Cu(2+) and Zn(2+) exposed mussels was elevated above the controls. Filtration and oxygen uptake rates were not correlated, but rather responded in different ways to metal pollution. While these physiological responses of P. perna may be of limited use in biomonitoring, they could indicate how populations may respond to marine pollution.

Correlations between metal uptake in the soft tissue of Perna perna and gill filament pathology after exposure to mercury

The accumulation of metal in soft tissues, filtration rate and gill filament morphology are correlated in the southern African rock mussel, Perna perna, during exposure to mercury (24 days) and recovery (24 days). The amount of Hg in soft tissues increased from 0.13 to 87.5 microg/g dry weight after 24 days exposure, and declined to 13 microg/g during recovery. Mean filtration rate fell from 3,979 to 1,818 ml/h/g dry weight by day 2, but recovered slightly through days 4 and 8 (3,037 ml/h/g), with a higher average rate (5,030 ml/h/g) being maintained over the 24-48 days recovery period. The initial decline in filtration coincided with epithelial cell deterioration presented as interstitial oedema, neural and epithelial cell degeneration and reduced ciliation. Between days 8 and 24, cilia regenerated and there was a general improvement in cell morphology. Gill filament morphology returned to near normal during the metal-free recovery period. The usefulness of P. perna as an indicator of pollution is discussed.

B-Myc is preferentially expressed in hormonally-controlled tissues and inhibits cellular proliferation

The myc family of genes plays an important role in several cellular processes including proliferation, apoptosis, differentiation, and transformation. B-myc, a relatively new and largely unstudied member of the myc family, encodes a protein that is highly homologous to the N-terminal transcriptional regulatory domain of c-Myc. Here, we show that high level B-myc expression is restricted to specific mouse tissues, primarily hormonally-controlled tissues, with the highest level of expression in the epididymis. We also report the identification of the endogenous B-Myc protein from mouse tissues. Like other Myc family proteins, B-Myc is a short-lived nuclear protein which is phosphorylated on residues Ser-60 and Ser-68. Rapid proteolysis of B-Myc occurs via the ubiquitin-proteasome pathway. Finally, we found that overexpression of B-Myc significantly slows the growth of Rat la fibroblasts and COS cells suggesting B-Myc functions as an inhibitor of cellular proliferation.

Disruption of Myc-tubulin interaction by hyperphosphorylation of c-Myc during mitosis or by constitutive hyperphosphorylation of mutant c-Myc in Burkitt's lymphoma

Somatic mutations at Thr-58 of c-Myc have been detected in Burkitt's lymphoma (BL) tumors and have been shown to affect the transforming potential of the Myc oncoprotein. In addition, the N-terminal domain of c-Myc has been shown to interact with microtubules in vivo, and the binding of c-Myc to alpha-tubulin was localized to amino acids 48 to 135 within the c-Myc protein. We demonstrate that c-Myc proteins harboring a naturally occurring mutation at Thr-58 from BL cell lines have increased stability and are constitutively hyperphosphorylated, which disrupts the in vivo interaction of c-Myc with alpha-tubulin. In addition, we show that wild-type c-Myc-alpha-tubulin interactions are also disrupted during a transient mitosis-specific hyperphosphorylation of c-Myc, which resembles the constitutive hyperphosphorylation pattern of Thr-58 in BL cells.

Mongolian gerbil (Meriones unguiculatus) as a model of cerebral infarction for testing new therapeutic agents

Stroke mortality represents the third leading cause of death worldwide, after coronary artery disease and cancer. It has been demonstrated that in Mongolian gerbils, a unilateral hemispheric cerebral infarction can be produced following unilateral occlusion of the carotid artery because of the absence of connecting arteries between the basilar and carotid systems in these animals. The objective of this study was to comprehensively characterize the model of cerebral infarction in gerbil, clinically, biochemically and especially morphologically for prospective use in testing new therapeutic agents. Cerebral infarction was produced by ligation of the left common carotid artery in experimental gerbils. The control animals were sham-operated. One hour after surgery, 0.5 ml of 1% trypan blue was administered intraperitoneally to all animals. Initial clinical evaluations were made 8 h after surgery and every day thereafter for 30 days. On each of days 10 and 30, 4 animals were sacrificed. The degree of cerebral infarction was evaluated on the basis of clinical response, electrolyte and enzyme changes, vascular permeability of blood-brain barrier and morphological alterations. The total post-infarction mortality rate was 50%. The clinical symptoms presented as ipsilateral hemiparesis, ptosis of the eyelid, circling behavior, decreased breathing rate, decreased blood pressure and increased heart rate. Such symptoms developed within 8 h of ligation and persisted to sacrifice at day 30. Creatine kinase increased significantly on the 10th day and remained high to day 30. Increased potassium from the damaged cells and breakdown of the blood-brain barrier were first detected 72 h post-infarction. The morphological data showed evidence of brain cell necrosis, autolysis and phagocytosis 10 and 30 days post-ligation in left hemispheres. Minor intercellular edema and some cell shrinkage was evident in the right brain. Areas of focal necrosis in the vicinity of blood vessels, especially in the left brain suggested a reperfusion injury as a consequence of minimal collateral reflow from the right brain into the left brain microvasculature. Experimental infarction in gerbil recreates the ischemic conditions causing stroke in humans. The animal model may be used for evaluating the efficacy of therapeutic agents that may ameliorate the condition in man.

c-Myc proteolysis by the ubiquitin-proteasome pathway: stabilization of c-Myc in Burkitt's lymphoma cells

The c-Myc oncoprotein is a transcription factor which is a critical regulator of cellular proliferation. Deregulated expression of c-Myc is associated with many human cancers, including Burkitt's lymphoma. The c-Myc protein is normally degraded very rapidly with a half-life of 20 to 30 min. Here we demonstrate that proteolysis of c-Myc in vivo is mediated by the ubiquitin-proteasome pathway. Inhibition of proteasome activity blocks c-Myc degradation, and c-Myc is a substrate for ubiquitination in vivo. Furthermore, an increase in c-Myc stability occurs in mitotic cells and is associated with inhibited c-Myc ubiquitination. Deletion analysis was used to identify regions of the c-Myc protein which are required for rapid proteolysis. We found that a centrally located PEST sequence, amino acids 226 to 270, is necessary for rapid c-Myc degradation, but not for ubiquitination. Also, N-terminal sequences, located within the first 158 amino acids of c-Myc, are necessary for both efficient c-Myc ubiquitination and subsequent degradation. We found that c-Myc is significantly stabilized (two- to sixfold) in many Burkitt's lymphoma-derived cell lines, suggesting that aberrant c-Myc proteolysis may play a role in the pathogenesis of Burkitt's lymphoma. Finally, mutation of Thr-58, a major phosphorylation site in c-Myc and a mutational hot spot in Burkitt's lymphoma, increases c-Myc stability; however, mutation of c-Myc is not essential for stabilization in Burkitt's lymphoma cells.

The complete genome sequence of the Streptomyces temperate phage straight phiC31: evolutionary relationships to other viruses

The completed genome sequence of the temperate Streptomyces phage straight phiC31 is reported. straight phiC31 contains genes that are related by sequence similarities to several other dsDNA phages infecting many diverse bacterial hosts, including Escherichia, Arthrobacter, Mycobacterium, Rhodobacter, Staphylococcus, Bacillus, Streptococcus, Lactobacillus and Lactococcus. These observations provide further evidence that dsDNA phages from diverse bacterial hosts are related and have had access to a common genetic pool. Analysis of the late genes was particularly informative. The sequences of the head assembly proteins (portal, head protease and major capsid) were conserved between straight phiC31, coliphage HK97, staphylococcal phage straight phiPVL, two Rhodobacter capsulatus prophages and two Mycobacterium tuberculosis prophages. These phages and prophages (where non-defective) from evolutionarily diverse hosts are, therefore, likely to share a common head assembly mechanism i.e. that of HK97. The organisation of the tail genes in straight phiC31 is highly reminiscent of tail regions from other phage genomes. The unusual organisation of the putative lysis genes in straight phiC31 is discussed, and speculations are made as to the roles of some inessential early gene products. Similarities between certain phage gene products and eukaryotic dsDNA virus proteins were noted, in particular, the primase/helicases and the terminases (large subunits). Furthermore, the complete sequence clarifies the overall transcription map of the phage during lytic growth and the positions of elements involved in the maintenance of lysogeny.

The evolution of biofilms in venous access devices implanted in children with Wilms' tumour

Biofilms form on all implanted foreign materials. In venous access ports (VAPs), the biofilm with entrapped organisms may be the source of recurring bacteraemia. At present, little is known of the development of biofilms in VAPs. In this study light, scanning, and transmission electron microscopy were used to investigate the evolution of biofilms in VAPs implanted in 15 African children with Wilms' tumour. The VAPs were removed either emergently because of infection (n = 6) or blockage (n = 3), or electively at the end of chemotherapy (n = 6). Intact biofilms were obtained from lengths of the catheter attached to ports that had been in place for 11 days to 3 years. Each was prepared for light and electron microscopy. In infected ports, shortly after implantation biofilms were thin and comprised of apparently healthy erythrocytes (RBCs) and occasional platelets, leucocytes (WBCs), and bacteria enmeshed in a network of fibrin. Three weeks after implantation, RBCs had autolysed and large numbers of WBCs and bacterial colonies were present within and on the luminal surface. In 1 instance, the lumen of a VAP had been occluded by a "plug" of WBCs. In non-infected patients, the biofilms in long-standing VAPs were of varying thickness and primarily composed of an amorphous granular material. In most cases, healthy and necrotic bacteria were present both within the core and on the surface of the biofilms. The results suggest that while bacteria, per se, are an important factor, the presence and degradation of blood components may be an equally important factor in the development of biofilms in VAP catheters.

Morphological aspects of microarterial anastomoses: a comparison of nylon with polydioxanone

The morphological appearance of longitudinally sectioned rat femoral arteries was determined in intact arteries and from 3 to 435 days after vessel division and anastomosis with either 9/0 gauge nylon or polydioxanone (PDS) in 26 animals. The purpose of the study was to establish the mechanisms and compare the quality of healing after microarterial anastomosis and to determine whether PDS was degraded before sufficient anastomotic healing had taken place. The results revealed that there was no difference in the process of healing or quality of anastomosis with either suture material. From 3 to 21 days post anastomosis, there was a progressive separation of the ends of vessels within the developing scar. Anastomotic patency was established and maintained at first by an adventitial overgrowth of fibroblasts and undifferentiated adventitial cells and later by the growth of a smooth myocyte scar that stretched between the cut ends of the vessel and over the intima in the form of elongated circumferential plaques. The vessel was morphologically healed by the 21st day. The sutures served little or no purpose in maintaining anastomotic integrity after the 5th day, being situated in the scar forming between the separating vessel ends. PDS was present within the vessel wall up to 120 days post anastomosis and was certainly intact at the time of morphological healing, suggesting that this material is safe as a microvascular suture.

The effects of hexane on rat myocardium: a morphometric and morphological study

Specimens from the left ventricular myocardium of 10 rats that had been exposed to subcutaneously administered hexane for 30 days were morphometrically and morphologically examined. Other than the presence of occasional necrotic fibres in hexane-treated animals, there was little difference in the histological appearance of myofibres in control or experimental specimens. There was a slight reduction in the average diameter of cardiac myofibres after exposure to hexane. Pathological ultrastructural changes of the myofibres were noted in the experimental and not in the control groups. Mitochondrial oedema and necrosis and myofilament disorganization and dissolution were significant changes noted in the experimental group. These pathological changes suggest that hexane, a constituent of glue and benzine, is cardiotoxic.

Serial morphological changes in primate skeletal myofibres after 3 hours of ischaemia and 24 hours of reperfusion

The sequential morphological changes occurring in skeletal myofibres after 3 hours' ischaemia and from 3 hours to 24 hours of reperfusion in vervet monkeys are described. Eight vervet monkeys were studied under general anaesthesia. A hind limb was exsanguinated and a tourniquet applied for 3 hours. Open muscle biopsy specimens were obtained from the tibialis anterior muscle before tourniquet application, just before tourniquet release and 3, 6, 12, 18 and 24 hours after tourniquet deflation. All specimens were prepared for transmission electron microscopy. After 3 hours of ischaemia and increasing periods of reperfusion, a small number of fibres showed progressive pathomorphological changes that eventually resulted in myofibre death. After initial glycogen loss and later intermyofibrillar oedema, the majority of myofibres returned to normal, while a group of fibres remained oedematous. The progressive morphological characteristics of reversibly injured myofibres undergoing repair and irreversible injured cells undergoing necrosis are described.

Alterations in the cytological composition of the juxta-scar villous mucosa after ulcer therapy with sucralfate or cimetidine

A comparative light-microscopic morphometric analysis of non-metaplastic mucosa obtained from the pretreatment juxta-duodenal ulcer (DU) villous mucosa of 10 patients and from the first part of the duodenum of 5 normal volunteers revealed a significant increase (P less than 0.01) in the number of goblet cells (GCs) per 100 microns of villous mucosa (GC/100 microns). Such an increase was thought to represent a mucoprotective response by the mucosa to the corrosive lumenal factors that may cause or maintain ulceration. A similar morphometric analysis was performed on the endoscopically healed juxta-scar villous mucosa of 11 patients successfully treated for 6 weeks with sucralfate (5 patients) or cimetidine (6 patients). After treatment with cimetidine, GC/100 microns was reduced to near-normal levels, whereas after sucralfate therapy it was significantly raised (P less than 0.05). The difference in GC/100 microns after treatment with either sucralfate or cimetidine was significant at the P less than 0.02 level. The apparent drug-mediated difference in the cytological composition of the healed mucosa was thought to be a function of the pharmacodynamic mechanisms of action of the two drugs in promoting DU healing. It is proposed that the retention of GC hyperplasia after curative therapy with sucralfate may predisposed patients so treated to extended periods of remission.

Plasma etomidate levels in mother and fetus

The most commonly used induction agent in anaesthesia for Caesarean section is still thiopentone. The increasing incidence of Caesarean section for delivery of premature babies from a hostile environment may call in question the assumption that the dose of thiopentone received by the neonate will not cause depression in the hours following birth. Previous studies on thiopentone for Caesarean section have shown inconsistency in umbilical vein/maternal vein ratios. We have studied plasma etomidate levels in maternal and umbilical blood at the time of delivery to see whether equilibrium occurs with this agent. We were able to demonstrate an umbilical/maternal vein etomidate ratio of 0.5 (SD 0.18), with no relation to time in the range encountered. Also, the uterine artery/uterine vein etomidate ratio was 0.86 (SD 0.33), suggesting that etomidate uptake into the fetus is effectively complete. Further, in all cases the neonatal plasma etomidate levels were less than half those measured at recovery of consciousness in adults in other studies, despite a larger induction dose than is usually used.

Alterations in the morphology of skeletal myofibres after 90 minutes of ischaemia and 3 hours of reperfusion

Morphometric, light and electron microscopic methods were employed to determine whether skeletal myofibres were damaged by 90 minutes of tourniquet-mediated ischaemia. Open biceps muscle biopsies were obtained before 90 minutes of upper limb tourniquet ischaemia in 5 Chacma baboons. Further biopsies were obtained just before tourniquet release in 2 animals and after 3 hours' reperfusion in the remaining 3 animals. Other than a slight reduction in myofibre diameter and the anaerobic depletion of intermyofibrillar glycogen, no pathological changes were noted in skeletal myofibres after ischaemia. However, after reperfusion there was myofibre enlargement, intermyofibrillar oedema, internalisation of nuclei, myofibrillar and mitochondrial disorganisation and dissolution, and Z-band streaming. These results show that reperfusion injury affects skeletal myofibres after 90 minutes of tourniquet-mediated ischaemia.

A histometric analysis of skeletal myofibers following 90 min of tourniquet ischemia and reperfusion

Routine tourniquet use causes sublethal hypoxic cellular injury and results in edema formation. Using a histochemical morphometric technique, edema caused by 90 min of tourniquet-induced ischemia and 3 hr of reperfusion is measured in the different muscle fibers of a primate model. The degree of cellular swelling is shown to be related to the fiber's metabolic dependence upon oxygen. After reperfusion, predominantly oxidative type 1 fibers show a 29% increase in diameter, P less than 0.0005, type 2a fibers which are both oxidative and glycolytic increase by 7%, P less than 0.005, and the glycolytic type 2b fibers increase by 5%, P less than 0.01. A 48% increase in interfiber distance occurs with reperfusion, P less than 0.01. By quantifying the different fibers' responses to ischemic injury, this method may be of use in investigating the pathophysiology and prevention of reperfusion injury and the post-tourniquet syndrome.

Disposition of propofol infusions for caesarean section

The disposition of propofol was studied in women undergoing elective Caesarean section. Indices of maternal recovery and neonatal assessment were correlated with venous concentrations of propofol. After induction of anaesthesia with propofol 2.0 mg.kg-1, ten patients received propofol 6 mg.kg-1.hr-1 with nitrous oxide 50 per cent in oxygen (low group) and nine were given propofol 9 mg.kg-1.hr-1 with oxygen 100 per cent (high group). Pharmacokinetic variables were similar between the groups. The mean +/- SD Vss = 2.38 +/- 1.16 L.kg-1, Cl = 39.2 +/- 9.75 ml.min-1.kg-1 and t1/2 beta = 126 +/- 68.7 min. At the time of delivery (8-16 min), the concentration of propofol ranged from 1.91-3.82 micrograms.ml-1 in the maternal vein (MV), 1.00-2.00 micrograms.ml-1 in the umbilical vein (UV) and 0.53-1.66 micrograms.ml-1 in the umbilical artery (UA). Neonates with high UV concentrations of propofol at delivery had lower neurologic and adaptive capacity scores 15 minutes later. The concentrations of propofol were similar between groups during the infusion but they declined at a faster rate in the low group postoperatively. Maternal recovery times did not depend on the total dose of propofol but the concentration of propofol at the time of eye opening was greater in the high group than the low group (1.74 +/- 0.51 vs 1.24 +/- 0.32 micrograms.ml-1, P less than 0.01). The rapid placental transfer of propofol during Caesarean section requires propofol infusions to be given cautiously, especially when induction to delivery times are long.

A morphological control for ventricular pathology in man: a morphometric and morphologic assessment of LV myofibres in secundum ASD

Ethical considerations preclude the biopsy of normal human myocardium. As a consequence, morphological investigations of diseased human heart muscle are hampered by a lack of suitable normal control tissue. The left ventricular (LV) myocardium of patients with isolated secundum atrial septal defect (ASD) is considered to be normal. This study was designed to investigate the possibility that the fine-structure of LV myofibres in hearts with ASD could be used as normal controls for myofibre pathomorphology. Wedge biopsies from the LV of four adults undergoing elective surgery for the repair of ASD were examined by light and electron microscopy. Bivariant myofibre morphometry showed that the LV myocardium of one specimen was 'normal' while three specimens exhibited varying degrees of hypertrophy. There was a correlation between the diameter (FD) and morphology of individual myofibres within and between specimens. In general, myofibres with FD less than 25 microns were similar in fine-structural appearance to those described as morphologically normal in animal models whereas those with FD greater than 25 microns exhibited hypertrophic features that increased in 'severity' with increase in myofibre size. It is proposed that although the LV myocardium in ASD may be mildly hypertrophied, myofibres with FD less than 25 microns are probably normal and may be used as fine-structural controls for myofibre pathomorphology in hearts suspected of disease.

Obstetric epidural analgesia with mixtures of bupivacaine, adrenaline and fentanyl

We performed a double-blind comparison of six solutions for epidural analgesia in 90 healthy Chinese women with uncomplicated pregnancies. Patients were randomly allocated to receive 10 ml bupivacaine 0.125% or 0.25% plain, bupivacaine 0.125% with adrenaline 1.25 micrograms/ml, bupivacaine 0.25% with adrenaline 2.5 micrograms/ml or the latter two solutions with added fentanyl 50 micrograms. Analgesia was unsatisfactory in 30% of the bupivacaine 0.125% groups without fentanyl. The addition of adrenaline, compared with bupivacaine 0.25% plain, gave faster onset and longer duration of analgesia (p less than 0.05) which was similar to that found in both fentanyl groups. There were no differences in method of delivery or neonatal Apgar scores among groups. The least concentrated mixture that gave the best analgesia was the combination of bupivacaine 0.125% with adrenaline 1.25 micrograms/ml and fentanyl 50 micrograms.

The addition of fentanyl to epidural bupivacaine in first stage labour

Epidural analgesia was studied in 100 healthy Chinese women with uncomplicated pregnancies in first stage labour. Patients were randomly allocated to receive 8 ml of one of the following five solutions: bupivacaine 0.125% with fentanyl 50 micrograms or fentanyl 100 micrograms, bupivacaine 0.25% plain, bupivacaine 0.25% with fentanyl 50 micrograms or fentanyl 100 micrograms. There was no difference in quality of analgesia among groups as measured by the reduction of visual analogue pain scores 20 minutes after the epidural dose. The duration of analgesia was similar among groups with the overall median duration being 105 minutes. There was no difference in method of delivery or neonatal Apgar scores. The least concentrated mixture providing good quality analgesia for the first stage of labour was the combination of bupivacaine 0.125% with fentanyl 50 micrograms.

Propofol infusion anaesthesia for caesarean section

Two propofol infusion regimens and a standard general anaesthetic were compared in thirty Chinese women undergoing elective Caesarean section. After induction of anaesthesia with propofol 2 mg.kg-1, ten patients received propofol 6 mg.kg-1.hr-1 and nitrous oxide 50 per cent in oxygen while ten were given propofol 9 mg.kg-1.hr-1 with 100 per cent oxygen. The other ten patients received thiopentone 4 mg.kg-1 and nitrous oxide 50 per cent in oxygen with enflurane one per cent. Maternal recovery times and psychomotor performance were recorded. Neonates were assessed by Apgar scores, neurologic and adapative capacity scores (NACS) and umbilical cord blood gas analysis. Haemodynamic changes were similar immediately following induction but the low propofol infusion group had the best haemodynamic stability subsequently. Recovery times were fastest in the low-infusion group but there were no differences in later postbox testing. Neonatal Apgar scores and umbilical blood gas analysis were similar but NACS at two hours were poorer in the high infusion group. A propofol infusion coupled with nitrous oxide appears to be a satisfactory technique for Caesarean section.

Effect of adrenaline on venous plasma concentrations of bupivacaine after interpleural administration

Bupivacaine 2.5 mg kg-1 (0.5 ml kg-1 of 0.5% solution), with or without adrenaline 5 micrograms ml-1, was administered by interpleural injection to 12 patients after elective cholecystectomy. Noncompartmental analysis indicated that the addition of adrenaline had no effect on total body clearance, apparent volume of distribution at steady state or elimination half-life of bupivacaine. However, peak plasma concentrations were lower in the adrenaline group (mean (SD) [range]: 2.57 (0.61) [1.52-3.11] vs 3.22 (0.27) [2.84-3.53] micrograms ml-1, P less than 0.05) and the time to maximum concentration was delayed (median [range]: 25 [15-30] vs 15 [10-20] min, P less than 0.05). Analgesia was variable and no differences were detected between the two groups. The addition of adrenaline appears prudent to minimize possible bupivacaine toxicity.

The haemodynamic effects of propofol and thiopentone for induction of caesarean section

Forty Chinese women for elective caesarean section received either propofol 2 mg.kg-1 or thiopentone 4 mg.kg-1 for induction of general anaesthesia. Systolic, mean and diastolic arterial pressures and heart rate were recorded non-invasively every minute for ten minutes. Post-induction arterial pressures were similar to pre-induction values with no differences between thiopentone and propofol. Following intubation, the rise in systolic arterial pressure was greater in the thiopentone group, 32.1 mmHg (SD 23.7) compared with the propofol group, 17.4 mmHg (SD 23.8), (P less than 0.05). In the thiopentone group, arterial pressures were slower in returning to baseline values. Heart rate was initially elevated in both groups to the same degree. At caesarean section, induction with propofol causes less variation in arterial pressure than thiopentone. Hypotension is probably prevented by the coincident stimulus of rapid sequence induction. Neonatal Apgar scores were similar between the two groups.

Maternal and fetal levels of propofol at caesarean section

Twenty women were given a bolus induction of propofol 2.0 mg.kg-1 for elective caesarean section. Induction to delivery times ranged from five to fourteen minutes. At delivery the maternal venous (MV) concentrations of propofol ranged from 0.53 to 1.48 micrograms.ml-1 umbilical vein (UV) 0.39 to 1.4 micrograms.ml-1 and umbilical artery (UA) 0.34 to 0.68 micrograms.ml-1 MV propofol concentrations were always higher than corresponding UV concentrations. The mean (95% confidence interval) UV/MV ratio was 0.65 (0.56-0.74) and the mean UA/UV ratio was 1.07 (0.99-1.15). Neither ratio was shown to be correlated with induction to delivery time. Distribution of propofol is rapid across the placenta and in the fetus. Apgar scores were higher with shorter incision to delivery times but were not correlated to umbilical levels of propofol.

Pharmacokinetics of propofol in women undergoing elective caesarean section

We have compared the pharmacokinetics of a bolus induction dose of propofol 2 mg kg-1 in 10 Chinese women undergoing elective Caesarean section with those in six non-pregnant Chinese women having laparoscopic sterilization. Blood propofol concentrations were measured using high pressure liquid chromatography with fluorimetric detection. Pharmacokinetic data were analysed by a model independent method based on statistical moment theory. Data from the laparoscopy group also underwent compartmental analysis, which produced similar kinetic results. Non-compartmental analysis estimated that the women undergoing Caesarean section had a similar elimination half-life (mean 81.27 (SD 18.87) min) and apparent volume of distribution at steady state (2.66 (0.63) litre kg-1) as non-obstetric patients (99.45 (29.40) min and 3.36 (1.87) litre kg-1). Clearance was more rapid in the Caesarean section group (39.32 (8.07) ml min-1 kg-1 vs 29.40 (8.72) ml min-1 kg-1) (P less than 0.05). The increased total body clearance may result from blood loss and delivery of the fetus and placenta at operation, although an increase in extrahepatic clearance is also possible.

Morphometric analysis to detect suspected myocardial disease. A pilot study

Myofibres in the normal left ventricle (LVs) of 24 healthy young accident victims and the diseased LVs of 10 subjects who died from constrictive pericarditis or congestive (African) cardiomyopathy were subjected to morphometric evaluation. Each myofibre was represented by a pair of measurements: cross-nuclear fibre (FD) and nuclear (ND) diameters. Using a VIDS image analyser interfaced with a light microscope, 150 paired measurements were determined for each of the 34 specimens. The bivariate relationship between FD and ND for each group of specimens were expressed as linear regressions. The limits for the group distribution of normal specimen FD/ND means were calculated and graphically depicted in the form of an ellipse. Disease specimens were plotted for comparison. Of the normal specimens, 23/24 FD/ND coordinates fell within the "normal' ellipse whereas the altered relationship between FD and ND in pathological myocardia caused all 10 specimen means to be plotted outside the ellipse and their regression lines to be displaced from normal. It is suggested that the normal data define the morphometric parameters of LV myofibres in healthy hearts and create a graphic standard by which myofibre pathology in hearts suspected of disease can be detected.