Substituted amylose as a matrix for sustained-drug release: a biodegradation study.

Substituted amylose polymers are prepared by reacting amylose chains with a suitable substituent such as 1,2-epoxypropanol (glycidol). Substituted amylose polymers are introduced as novel excipients for controlled release of bioactive materials. Since substituted amylose polymers are amylose-based polymers, they are subject to biodegradation by alpha-amylase enzymes present in the gastro-intestinal tract; thus, gamma spectroscopy is used to follow the release of the natural abundant rhenium (VII) oxide used as a drug model, and to test their resistance to alpha-amylase enzymatic degradation. Two substituted amylose solid dosage forms were prepared: (i) matrix system and (ii) dry-coated tablets. Matrix systems and dry-coated tablets maintained their structure, and controlled the release of [186Re] showing no significant degradation of tablets by alpha-amylase.

Effects of the D2 receptor agonist bromocriptine on sleep bruxism: report of two single-patient clinical trials.

An altered dopamine receptor status has been associated with sleep bruxism. Evidence from a functional neuro-imaging study has implicated an abnormal side imbalance in striatal D2 receptor expression in its pathophysiology. To assess the significance of this finding, we studied the effects of short-term administration of the preferential dopamine D2 receptor agonist bromocriptine on sleep bruxism in a double-blind, placebo-controlled polysomnographic and neuro-imaging study with a single crossover design. Six otherwise healthy and drug-free patients with sleep bruxism were entered into the trial. One of the patients dropped out due to an intercurrent illness, while three others were discontinued from the study due to severe adverse reactions to bromocriptine. Because of the high frequency and intensity of the side-effects, the trial was interrupted. Two patients, however, completed the trial without any adverse reactions. Their outcome measures are presented as single-patient clinical trials. Following a two-week administration of bromocriptine, both patients showed a decrease in the number of bruxism episodes per hour of sleep of about 20% to 30% with respect to the placebo. WHile no significant differences between both conditions (i.e., placebo and bromocriptine) were found for the number of bruxism bursts per episode, significantly lower root-mean-squared EMG levels per bruxism burst occurred during bromocriptine use. In association with this polysomnographically established attenuation of sleep bruxism, bromocriptine afforded a decreased normal side distribution of striatal D2 receptor binding, as was evidenced by single-photon-emission computed tomography using the radioactive D2 receptor antagonist iodine-123-iodobenzamide. This study supports previous suggestions that the central dopaminergic system may be involved in the modulation of sleep bruxism. To see if the present findings apply across a population, investigators should use a peripheral D-2 antagonist to prevent side-effects.

Technetium-99m-tetrofosmin as a substrate for P-glycoprotein: in vitro studies in multidrug-resistant breast tumor cells.

UNLABELLED: The accumulation of 99mTc-tetrofosmin (TFos) was studied in wildtype (WT) and doxorubicin-resistant (AdrR) variants of the rat MatB and human MCF-7 breast tumor cell lines to determine whether TFos, like 99mTc-sestamibi (MIBI), is a substrate for P-glycoprotein (P-gp), a multidrug-resistance transporter. METHODS: The time course of accumulation of TFos and MIBI in WT and AdrR cells over 1 hr was studied using single-cell suspensions at 1 x 10(6) cells/ml incubated at 37 degrees C in the presence or absence of PSC833, a potent modulator of P-gp. Modulator dose-response curves were generated for PSC833, cyclosporin A, and verapamil. RESULTS: In both MatB and MCF-7 cells, TFos and MIBI accumulated extensively in WT cells and accumulation was not affected by PSC833. In contrast, ADrR cell lines accumulated very little of either tracer, but addition of PSC833 or other modulator increased this accumulation in a dose-dependent fashion. TFos and MIBI did not differ significantly in their behavior. CONCLUSION: TFos shares with MIBI the property of being a substrate for P-gp and thus TFos may be useful for functional imaging of tumor P-gp status.

Myocardial kinetics of technetium-99m teboroxime in the presence of postischemic injury, necrosis and low flow reperfusion.

OBJECTIVES: This study evaluated technetium-99m (Tc-99m) teboroxime kinetics in postischemic and partially necrotic myocardium with complete and low flow reperfusion using an isolated perfused rat heart model. BACKGROUND: Technetium-99m teboroxime has been proposed for use in the early diagnosis of reperfusion after thrombolysis on the basis of models of myocardial necrosis with complete reperfusion. Clinically, however, reperfusion is frequently incomplete, resulting in a mixture of necrotic, ischemic and postischemic tissue. METHODS: Hearts were classified into five groups: group 1 (n = 8, control); group 2 (n = 7, 30 min of no flow with complete reperfusion); group 3 (n = 12, 60 min of no flow to induce partial necrosis, followed by complete reperfusion); group 4 (n = 8, continuous low flow without flow interruption); and group 5 (n = 9, 60 min of no flow with low flow reperfusion). Buffer containing Tc-99m teboroxime was perfused for 15 min, followed by tracerfree buffer for 35 min, to evaluate uptake and clearance, respectively. RESULTS: Uptake slopes for groups 1 to 5 were (mean +/- SD) 3.0 +/- 0.7, 2.6 +/- 0.8, 2.1 +/- 0.5, 0.8 +/- 0.2 and 0.8 +/- 0.3, respectively (p < or = 0.0005 for groups 1, 2 and 3 vs. groups 4 and 5, and p = 0.003 for group 3 vs. groups 1 and 2). Clearance curves from groups 1 to 3 were best fit by a biexponential function (p < 0.001); those from groups 4 and 5 were monoexponential. In groups 1, 2 and 3, the initial clearance rate constants (ki) (0.9 +/- 0.5 x 10(-3); 1.0 +/- 0.2 x 10(-3); 1.1 +/- 0.5 x 10(-3) s-1, respectively) and the monoexponential rate constants (Kmono) (2.0 +/- 0.3 x 10(-4); 2.2 +/- 0.4 x 10(-4); 2.1 +/- 0.2 x 10(-4) s-1, respectively) were significantly greater than those in groups 4 and 5 (0.9 +/- 0.5 x 10(-4); 1.2 +/- 0.3 x 10(-4) s-1, respectively, p < or = 0.005). CONCLUSIONS: The uptake and initial clearance kinetics of Tc-99m teboroxime depend mainly on myocardial flow in this model. The presence of partial necrosis and postischemic injury has little effect on the initial clearance but leads to some reduction in uptake at normal flow rates. Evaluation of Tc-99m teboroxime kinetics may permit early noninvasive detection of inadequate reperfusion in acute myocardial infarction.

Nephrotoxicity of ioxaglate and ioversol assessed by glomerular filtration rate: a pilot study.

OBJECTIVE: To determine the effect of ioxaglate and ioversol on glomerular filtration rate (GFR) in a heterogeneous inpatient group to allow calculation of the necessary sample size for a randomized trial. PATIENTS AND METHODS: The study group consisted of 36 men and 12 women, ranging in age from 25 to 79 (mean 63) years. Fourteen of the patients, those undergoing abdominal aortography with or without renal arteriography, received ioxaglate (Hexabrix 320; 40 to 240 [mean 141] mL), and the remaining 34, those receiving intravenous injections and those undergoing computed tomography with arterioportography or carotid arteriography, received ioversol (Optiray 320; 20 to 180 [mean 87] mL). GFR was measured by determining the clearance of diethyl-enetriaminepenta-acetic acid labelled with technetium-99m up to 72 hours before and 24 hours after administration of the contrast medium. Risk factors for nephrotoxicity included diabetes (7 patients) and pre-existing renal impairment (mild in 11 and severe in 6). RESULTS: GFR decreased by 20% to 34% in six patients (13%); in only one of these was the serum level of creatinine increased at 24 hours. One of these six patients had received 120 mL of ioversol for carotid arteriography and had no risk factors for nephrotoxicity. The other five had received 40 to 187 (mean 115) mL of ioxaglate, three for abdominal aortography and two for selective renal arteriography. The risk factors in these patients included diabetes (two patients) and severe pre-existing renal impairment (two patients). Renal failure necessitating treatment did not develop in any of the patients. CONCLUSIONS: A decrease in GFR occurred more often with ioxaglate than with ioversol and usually occurred in patients with additional risk factors. Injection of contrast medium into the abdominal aorta or the renal artery may increase the risk of nephrotoxicity. Changes in serum level of creatinine at 24 hours were not reliable in identifying patients with decreased GFR. On the basis of these data, the authors estimate that a group of 194 patients would be necessary for a randomized trial comparing the nephrotoxicity of ioxaglate and ioversol for abdominal aortography.

meta-iodobenzylguanidine uptake in the hypertensive-diabetic rat heart: a marker for myocardial dysfunction?

The purpose of this study was to investigate the cardiac adrenergic neuronal changes induced by diabetes and hypertension by using an analogue of norepinephrine, meta-iodobenzylguanidine (MIBG), and to compare these changes with the contractile state of ventricular papillary muscle. The tissue concentration of norepinephrine in the cardiac apex was also measured for direct comparison with [123I]MIBG uptake. One week following the induction of diabetes by streptozotocin injection (55 mg/kg, i.v.), male Sprague-Dawley rats were given subcutaneous injections of a hypertension-inducing agent, deoxycorticosterone acetate (DOCA, 25 mg/kg), or DOCA vehicle twice weekly for 3, 6, 9, or 12 weeks. At the end of each time point, the animals were injected intravenously (15 mCi/mg; 1 Ci = 37 GBq) with [123I]MIBG. The results showed a progressive decrease in MIBG uptake into the hearts of diabetic, hypertensive, and diabetic-hypertensive rats during the 12-week observation period, compared with the control group. However, length-tension papillary muscle studies at 12 weeks indicated that only the diabetic group had a diminished performance compared with control. Furthermore, an inverse relationship was observed between MIBG uptake and norepinephrine levels in the cardiac apex of the diabetic and diabetic-hypertensive groups. Therefore, we concluded that either MIBG does not provide an accurate indication of adrenergic integrity or that there is no relationship between sympathetic activity and myocardial function at the time points measured. MIBG did not prove to be a useful marker for myocardial dysfunction in diabetic rats.

In vivo inhibition of beta-glucosidase and beta-mannosidase activity in rats by 2-deoxy-2-fluoro-beta-glycosyl fluorides and recovery of activity in vivo and in vitro.

2-Deoxy-2-fluoro-beta-glucosyl and -beta-mannosyl fluorides administered to rats in a single dose (10 mg/kg) inhibited beta-glucosidase and beta-mannosidase activity respectively after 1 h in brain, spleen, liver and kidney tissues. This inhibition, presumably caused by accumulation of 2-deoxy-2-fluoroglycosyl-enzyme intermediates, indicates that intact 2-deoxy-2-fluoroglycosyl fluorides are distributed to these organs and, in the case of brain, that they cross the blood/brain barrier. beta-Glucosidase activity recovered completely or partially in brain, spleen, liver and kidney by 20-48 h. beta-Mannosidase activity partially recovered in all tissues by 48 h. beta-Galactosidase activity in brain and kidney was not significantly affected by administration of either the gluco or manno compounds at this dosage, indicating that these inhibitors are directed towards specific glycosidases. Observation of similar relatively rapid rates of beta-glycosidase re-activation in vivo and in tissue homogenates in vitro at 37 degrees C suggests that hydrolysis or transglycosylation of 2-deoxy-2-fluoroglycosyl-enzymes, not protein synthesis, are the primary mechanisms involved in the recovery of glycosidase activity inhibited by this class of compounds in vivo.

Reproducibility of plasma and extracellular fluid volume measurements in critically ill patients.

Plasma and extracellular fluid (ECF) volume measurements may provide valuable complementary data to the hemodynamic measurements currently used to compare fluid infusions in critically ill patients. To assess the reproducibility of plasma and extracellular fluid volume measurements in critically ill patients, we injected 131I-labeled albumin (10 microCi) and 35S-sodium sulfate (50 microCi), respectively, into 15 stable patients on two occasions 150 min apart. Plasma was sampled at 20, 30, and 40 min after each injection and the volume of distribution of each radioisotope was calculated from the extrapolated zero time counts. We found that plasma and ECF volume did not differ significantly between the first (42.4 +/- 4.7 ml/kg and 186 +/- 39 ml/kg) and second (42.8 +/- 5.5 ml/kg and 193 +/- 48 ml/kg) measurements. Specifically, the mean difference between the two measurements was 0.4 +/- 3.2 ml/kg and 7 +/- 17 ml/kg respectively. We conclude that measurements of plasma and ECF volume are reproducible over 150 min in stable critically ill patients.

Noninvasive detection of Helicobacter pylori colonization in stomach using [11C]urea.

Helicobacter pylori is associated with chronic type B gastritis. Diagnosis can be made on gastric biopsy specimens and noninvasively using [13C]- or [14C]urea breath tests. Both breath tests require meticulous breath collection, and false positive results are possible from urease producing oral-pharyngeal flora. We used [11C]urea, a positron-emitting radionuclide allowing dynamic imaging, to measure metabolism of urea in the stomach of biopsy documented H. pylori-positive patients. [11C]urea was synthesized from 11CO2 produced using a Van de Graaff accelerator and administered with [99mTc]DTPA to control for loss of radioactivity via gastric emptying. Images were obtained externally by gamma camera every minute and 11CO2 was monitored in the breath continuously for 30 min. An H. pylori-positive patient exhibited a 99mTc/11C activity ratio of 2:1 in the stomach 10-20 min following administration, compared to a 1:1 ratio in a negative control, indicating metabolism of urea to 11CO2 with subsequent diffusion of 11C activity out of the stomach. The 11C activity in the breath peaked at 10-20 min in the H. pylori-positive patients. The short half-life of carbon-11 (20.4 min) alleviates radiation safety concerns and results in low absorbed radiation doses to patients.

Doxorubicin-3'-NH-oestrone-17-oxime-ethyl-carbonyl, a doxorubicin-oestrone conjugate that does not redox cycle in rat liver microsomes.

In summary doxorubicin-3'-NH-oestrone-17-oximethyl-carbonyl (Dox-Oes) is a covalent adduct of the anthracycline antitumor agent doxorubicin and oestrogen. Dox-Oes does not generate free radicals in rat liver microsomes as detected by electron spin resonance spectroscopy or redox cycle as shown by lack of superoxide anion formation and NADPH oxidation. Furthermore Dox-Oes actually inhibits free radical formation by doxorubicin used in equimolar amounts. The lack of free radical formation by doxorubicin when covalently linked to oestrone supports the development of Dox-Oes as a non-cardiotoxic derivative whilst potentially improving its targeting to oestrogen positive breast tumour cells.

Binding of actinomycin D to DNA: evidence for a nonclassical high-affinity binding mode that does not require GpC sites.

We have employed a combination of temperature-dependent UV absorption spectroscopy, circular dichroism, and batch calorimetry to characterize the binding of actinomycin D to a series of oligomeric DNA duplexes. We find the duplex [d(CGTCGACG)]2 to be unique in its ability to bind actinomycin D strongly despite the absence of a classic GpC site. We present evidence that this non-GpC-containing duplex binds two actinomycin D molecules in an apparently cooperative manner to form a complex that exhibits aberrant spectroscopic and calorimetric behavior. We propose that these observations are consistent with actinomycin D exhibiting a high-affinity, sequence-dependent DNA-binding mode distinct from its classic binding to isolated GpC sites.