Efficacy of artemisinin and mefloquine combinations against Plasmodium falciparum. In vitro simulation of in vivo pharmacokinetics

The activity of artemisinin in combination with mefloquine was tested in vitro against a chloroquine-sensitive (F32) strain of Plasmodium falciparum. A method of repetitive dosing and extending the culture observation period to 28-30 days was used to mimic the in vivo pharmacokinetic situation. Plasmodium falciparum was exposed to artemisinin from 10(-8) to 10(-5) M, mefloquine from 3 x 10(-9) to 10(-5) M and their combinations. The exposure time for artemisinin was 3 hours twice daily and for mefloquine 24 hours. The drug-dosing duration was 3 days. Neither artemisinin nor mefloquine alone provided radical clearance of P. falciparum, even when maximum concentrations (10(-5) M) were applied. The antiparasitic activity of artemisinin and mefloquine were significantly higher when dosed alone. Effective concentrations for different degrees of inhibition (EC 50, 90 and 99) of both artemisinin and mefloquine respectively were significantly lower when used in combination. At concentrations normally reached in vivo, this effect was clearly synergistic (P = 0.016) Our in vitro model of intermittent dosing of artemisinin and mefloquine combinations for 3 days provides significant evidence of positive interaction between the two compounds. Lower combination concentrations around the MIC-values for the individual compounds showed synergistic effect, and high concentrations showed additive effect. This indicates that such drug combinations may provide radical clearance at concentrations lower than those required for single-drug treatment.     

Intraperitoneal hyperthermic treatment of implanted peritoneal cancer in rats

The feasibility and efficacy of treating peritoneal cancer implants by applying heat to the peritoneal surfaces were studied in inbred Buffalo A rats given i.p. injections of Morris hepatoma 5123TC tumor cells. Heat was delivered to the peritoneum by contact with a heated physiological salt solution (Normosol-R) in the peritoneal cavity. A treatment temperature of 43.3 +/- 0.3 degrees was maintained for 30 min by an immersed stainless steel coil through which hot liquid circulated. Rats implanted with 0.5 to 1.0 x 10(8) tumor cells were treated at 1 to 4 hr (Group I), 4 to 5 days (Group II), and 22 to 24 days (Group III) after tumor implantation to simulate treatment for the clinical conditions of surgically spilled cancer cells, established microscopic cancer implants, and macroscopic cancer implants, respectively. A statistically significant improvement in survival was observed in Groups I and II compared with sham-treated control animals; 58% of the heat-treated animals were cured. Only a slight but statistically insignificant improvement was noted in Group III. These observations indicate that i.p. surface heat treatment of peritoneal implanted cancer is feasible and effective.     

The dynamic regulation of myocardial oxidative phosphorylation: analysis of the response time of oxygen consumption

Although usually steady-state fluxes and metabolite levels are assessed for the study of metabolic regulation, much can be learned from studying the transient response during quick changes of an input to the system. To this end we study the transient response of O2 consumption in the heart during steps in heart rate. The time course is characterized by the mean response time of O2 consumption which is the first statistical moment of the impulse response function of the system (for mono-exponential responses equal to the time constant). The time course of O2 uptake during quick changes is measured with O2 electrodes in the arterial perfusate and venous effluent of the heart, but the venous signal is delayed with respect to O2 consumption in the mitochondria due to O2 diffusion and vascular transport. We correct for this transport delay by using the mass balance of O2, with all terms (e.g. O2 consumption and vascular O2 transport) taken as function of time. Integration of this mass balance over the duration of the response yields a relation between the mean transit time for O2 and changes in cardiac O2 content. Experimental data on the response times of venous [O2] during step changes in arterial [O2] or in perfusion flow are used to calculate the transport time between mitochondria and the venous O2 electrode. By subtracting the transport time from the response time measured in the venous outflow the mean response time of mitochondrial O2 consumption (tmito) to the step in heart rate is obtained. In isolated rabbit heart we found that tmito to heart rate steps is 4-12 s at 37 degrees C. This means that oxidative phosphorylation responds to changing ATP hydrolysis with some delay, so that the phosphocreatine levels in the heart must be decreased, at least in the early stages after an increase in cardiac ATP hydrolysis. Changes in ADP and inorganic phosphate (Pi) thus play a role in regulating the dynamic adaptation of oxidative phosphorylation, although most steady state NMR measurements in the heart had suggested that ADP and Pi do not change. Indeed, we found with 31P-NMR spectroscopy that phosphocreatine (PCr) and Pi change in the first seconds after a quick change in ATP hydrolysis, but remarkably they do this significantly faster (time constant approximately 2.5 s) than mitochondrial O2 consumption (time constant 12 s). Although it is quite likely that other factors besides ADP and Pi regulate cardiac oxidative phosphorylation, a fascinating alternative explanation is that the first changes in PCr measured with NMR spectroscopy took exclusively place in or near the myofibrils, and that a metabolic wave must then travel with some delay to the mitochondria to stimulate oxidative phosphorylation. The tmito slows with falling temperature, intracellular acidosis, and sometimes also during reperfusion following ischemia and with decreased mitochondrial aerobic capacity. In conclusion, the study of the dynamic adaptation of cardiac oxidative phosphorylation to demand using the mean response time of cardiac mitochondrial O2 consumption is a very valuable tool to investigate the regulation of cardiac mitochondrial energy metabolism in health and disease.     

Dominant T-cell clones of unknown significance in patients with idiopathic sensory neuropathies

The aim of this study was to describe an high-performance liquid chromatographic assay for the simultaneous determination of two HIV protease inhibitors, saquinavir and ritonavir, in human serum. The method involved extraction of ritonavir and saquinavir from serum with the aid of solid-phase extraction C18 cartridges followed by high-performance liquid chromatography with a C8 column and ultraviolet detection set at a wavelength of 240 nm. The assay was linear and has been validated over the concentrations range of 0.5-32 microg/ml for ritonavir and 0.075-4.8 microg/ml for saquinavir, from 600 microl serum extracted. In future, the assay will be used to support human population pharmacokinetic studies, and therapeutic drug monitoring for ritonavir and saquinavir.     

Genetic transformation of germinated conidia of the thermophilic fungus Humicola grisea var. thermoidea to hygromycin B resistance

Dihydrotestosterone decreased alcohol dehydrogenase (ADH) activity and enzyme-protein in rat hepatocytes in culture. This effect was observed after the hepatocytes had been exposed to dihydrotestosterone for 3 days at concentrations of 0.5 micromol/L or higher. Dihydrotestosterone did not decrease alcohol dehydrogenase messenger RNA (mRNA) but, rather, resulted in small increases in ADH mRNA after 3 days of exposure. To further determine the mechanism for the effects of dihydrotestosterone in decreasing the enzyme, the turnover of ADH was determined after incorporation of [3H]-leucine into the enzyme protein. Dihydrotestosterone did not alter the initial 2-hour incorporation of [3H]-leucine into the enzyme protein. Dihydrotestosterone, however, resulted in an increase in the fractional rate of degradation (Kd) of the enzyme from 0.12 +/- 0.013 to 0.23 +/- 0.004 per hour (P < .001) accompanied by a much smaller increase in the fractional rate of synthesis (Ks) from 0.12 +/- 0.028 to 0.17 +/- 0.031 per hour (P > .05). Hence, the mechanism for the fall in ADH in the presence of dihydrotestosterone is an increase in enzyme degradation which is not accompanied by a sufficient increase in enzyme synthesis.     

The effect of plasma drug concentrations on HIV-1 clearance rate during quadruple drug therapy

OBJECTIVE: To investigate the relationship between exposure to antiretroviral drugs and the initial decline of plasma HIV-1 RNA. DESIGN: Open-label study in antiretroviral-naive HIV-1 infected patients using a quadruple drug regimen [nelfinavir (NFV), saquinavir (SQV), stavudine, and lamivudine]. METHODS: The elimination rate constant (k) for HIV-1 clearance was calculated during the first 2 weeks of treatment in 29 patients. Exposure to NFV and SQV was quantified on each study visit. Observed NFV and SQV concentrations were related to those expected in a reference population and a concentration ratio was calculated. The median concentration ratios for NFV and SQV, the baseline CD4+ lymphocyte count and baseline log10 HIV-1 RNA were correlated with k. RESULTS: A significant positive correlation was observed between k and the median NFV (P = 0.001) or SQV concentration ratio (P = 0.016) in univariate analysis. In multivariate analyses, the median NFV concentration ratio remained significantly correlated with k. CONCLUSIONS: The variation in the rate of decline of plasma HIV-1 RNA between patients after the initiation of a quadruple drug regimen could be explained by differences in exposure to NFV or SQV. Determination of k could be used to optimise further antiretroviral drug therapy and may be a first tool to assess antiretroviral activities of new or increasing doses of drugs administered in combination regimens. Furthermore, our data suggest that exposure to antiretroviral drugs should be incorporated in mathematical models to describe HIV-1 dynamics in more detail.     

Outcomes of high-dose unilateral kidney irradiation in patients with gastric lymphoma

PURPOSE: To review the long-term clinical effects of unilateral kidney irradiation on overall renal function and blood pressure in patients with gastric lymphoma. METHODS AND MATERIALS: In the study were 27 patients with Stage I or II gastric lymphoma who had undergone irradiation of at least 24 Gy to > or = 1/3 of the left kidney. They include 16 women and 11 men, aged 31 to 77, with a mean age of 57.6 years (median 56). Fifteen patients had Stage I and 12 had Stage II disease. In 13 patients the whole kidney had been irradiated, and 14 had had partial kidney irradiation, at doses ranging between 24 and 40.5 Gy. All patients received combined chemotherapy with various drugs: all patients received corticosteroids, and five received cis-platinum. Their follow-up ranged between 0.7 and 7.8 years (mean 3.4 years). Data on possible effects of the treatment on blood pressure, renal function as assessed by blood urea and creatinine, and kidney shrinkage as seen by serial computed tomography scanning were collected on all patients. RESULTS: Three patients had persistent, mild elevations of urea and creatinine levels, which did not require special treatment. All three also received cis-platinum. Ipsilateral kidney shrinkage was evident in most patients. In 19 patients the craniocaudal measurement of the kidney shrank by > or = 1.6 cm. Shrinkage in other dimensions was also evident. The degree of atrophy was related to the volume of kidney irradiated. Only two patients developed hypertension, both at a low level of 150/90; one patient had had 40 Gy to the whole kidney, the other 40 Gy to half the kidney. Neither patient had elevated urea or creatinine. CONCLUSIONS: Notwithstanding the shrinkage to the irradiated part of the kidney, the treatment did not lead to clinically significant hypertension or renal dysfunction. The administration of cis-platinum to patients with gastric lymphoma that requires kidney irradiation should be further evaluated.     

Cytokines and the microcirculation in ischemia and reperfusion

The intense inflammatory reaction following reperfusion of the infarcted myocardium has been implicated as a factor in extension of injury. However, this inflammatory reaction is also critical to tissue repair. The cellular responses that mediate these functions are orchestrated by sequential induction and/or release of cytokines resulting in a closely regulated cytokine cascade. This paper reviews research on these cytokine cascades, their cellular origin, and factors which control the cellular response to their presence. Factors examined include leukotaxis, phenotypic transition of leukocytes, adhesion molecule induction and the role of cytokines in tissue repair and scar formation.