Relative bioavailability and pharmacokinetic comparison of calcium glucoheptonate with calcium carbonate

Adequate calcium intake is important for the prevention of bone loss and osteoporosis. For some populations such as those of Southeast Asia where calcium intake is very low, supplements represent a suitable dietary source of calcium. The objective of this study was to compare the relative oral bioavailability of calcium from calcium glucoheptonate, a highly soluble calcium salt containing 8.2% of elemental calcium, to that of calcium carbonate. A single-dose, randomized-sequence, open-label, two-period crossover study, with a 7-day washout period, was conducted in 24 Indonesian healthy adult volunteers. After a 12-hour (overnight) fast, subjects received either two oral ampoules of 250 mg/10 mL of calcium glucoheptonate each or one effervescent tablet of calcium carbonate containing 500 mg of elemental calcium. The relative oral bioavailability of calcium from calcium glucoheptonate as compared to calcium carbonate was 92% within 6 hours and 89% within 12 hours after study drug administration. The 90% confidence intervals for the mean test/reference ratios of the maximum plasma concentration and the area under the concentration-time curve at 12 hours post-administration were 77.09%-120.31% and 60.58%-122.30%, respectively. Five subjects experienced a total of eight adverse events which were all mild and transient; no serious adverse events or deaths were reported. These results indicate that calcium glucoheptonate is associated with a high relative bioavailability of calcium compared to calcium carbonate, and is well-tolerated. Calcium glucoheptonate might thus be a potential choice for calcium supplementation in Southeast Asian populations.

Non-invasive assessment of blood-brain barrier (BBB) permeability using a gamma camera to detect 99technetium-gluceptate extravasation in rat brain

The blood-brain barrier (BBB) is a complex structure of endothelial cells, astroglia, pericytes, and perivascular macrophages enclosed by basal lamina. The BBB regulates the entry of blood-borne molecules and cells into the brain, but it is disrupted in various inflammatory conditions of the central nervous system (CNS). We previously showed that 30 min of immobilization stress increased 99technetium-gluceptate (99Tc) extravasation, measured by a gamma counter, in brain regions containing mast cells, an effect blocked by the mast cell stabilizer disodium cromoglycate [Brain Res. 888 (2001) 117]. Here we report the use of a gamma camera to assess BBB permeability by assessing 99Tc extravasation in the rat brain, during and following acute stress, without having to sacrifice the experimental animals. This method also allows for repeated experimentation on the same animal, since the half-life of 99Tc is only 6 h, and permits testing of potential inhibitors of BBB permeability.

Acute stress increases permeability of the blood-brain-barrier through activation of brain mast cells

Disruption of the blood-brain-barrier (BBB) is important in the pathophysiology of various inflammatory conditions of the central nervous system (CNS), such as multiple sclerosis (MS), in which breakdown of the BBB precedes any clinical or pathological findings. There is some evidence that relapsing-remitting MS attacks may be correlated with certain types of acute stressful episodes. Stress typically activates the hypothalamic-pituitary-adrenal (HPA) axis through the release of corticotropin releasing hormone (CRH), leading to production of glucocorticoids that down regulate immune responses. However, acute stress also has pro-inflammatory effects that appear to be mediated through activation of mast cells. Here we show that acute stress by immobilization increased permeability of rat BBB to intravenous 99Technetium gluceptate (99Tc). This effect was statistically significant in the diencephalon and the cerebellum, while it was absent in the cerebral cortex where there are not mast cells. Immobilization stress also induced activation of mast cells in diencephalon, the site where most mast cells are found in the rat brain. Both BBB permeability and mast cell activation were inhibited by the 'mast cell stabilizer' disodium cromoglycate (cromolyn). These results expand the pathophysiology of mast cells and implicate them in CNS disorders, that may possibly be induced or exacerbated by stress.

The effect of vincristine on the biodistribution of technetium-99m DTPA, GHA, and DMSA in Balb/c female mice

OBJECTIVE

Vincristine has been widely used in various chemotherapeutic protocols in oncology. The purpose of this study was to evaluate the effect of vincristine on the biodistribution of 99mTc-DMSA, 99mTc-GHA, and 99mTc-DTPA in Balb/c female mice.

METHODS

Vincristine (0.03 mg, 0.3 mL) was injected into female isogenic Balb/c mice (n = 15), in 3 doses over an interval of 96 h. The 99mTc-DMSA, 99mTc-GHA, or 99mTc-DTPA (7.4 MBq) was administered after the last dose of vincristine. After 0.5 h the animals were killed rapidly. The organs (pancreas, thyroid, brain, thymus, ovary, uterus, spleen, kidney, heart, stomach, lung, liver, bone, and lymph nodes) were isolated and the radioactivity in each organ was counted in a NaI(Tl) well counter. The percentage of radioactivity (%) in each was calculated and compared with the control group. Statistical analysis was performed by Wilcoxon test (P < 0.05).

RESULTS

The percentage of 99mTc-DMSA was increased in the lung, pancreas, heart, thyroid, brain, bone, and lymph nodes (inguinal and mesenteric). The percentage of 99mTc-GHA was decreased in the uterus, ovary, spleen, thymus, lymph nodes (inguinal and mesenteric), kidney, and heart. The percentage of 99mTc-DTPAwas increased in thymus, lymph nodes (inguinal and mesenteric), ovary, uterus, spleen, kidney, heart, stomach, lung, liver, and bone.

CONCLUSION

The results could be explained by the metabolization, toxic effect, therapeutic, or immunosupressive action of the studied chemotherapeutic drug.

Assessment of the effect of vincristine on the biodistribution of 99Tcm-labelled glucoheptonic acid in female Balb/c mice

There is evidence that the biodistribution and the pharmacokinetics of 99Tcm radiopharmaceuticals can be modified by some drugs, pathological states, irradiation and surgical procedures. Vincristine have been widely used in various chemotherapeutic protocols in oncology. We are trying to develop an animal model to assess the toxicology in different organs of compounds used as therapeutic drugs. We have studied the effect of vincristine on the distribution of 99Tcm-glucoheptonic acid (99Tcm-GHA) in female mice. After the last dose of vincristine, 99Tcm-GHA (7.4 MBq) was injected, the animals sacrificed and the percentage of radioactivity determined in the isolated organs. The percentage of activity was significantly decreased in the uterus, ovary, spleen, thymus, lymph nodes (inguinal and mesenteric), kidney and heart, but was not significantly altered in the lung, liver, pancreas, stomach, thyroid, brain and bone. Our results can be explained by the metabolic, toxic, therapeutic and immunosuppressive actions of this chemotherapeutic drug.

Gene transfer for targeted modification of salmonid fish metabolism

The reviewed studies addressed the possibility of using gene transfer for correction of L-ascorbic acid biosynthesis and carbohydrate utilization in rainbow trout. Analyses of enzymatic activities in the L-AAB pathway indicated that reasons for the lack of L-AA production can be common in fish and scurvy-prone animals. Rat gulonolactone oxidase cDNA was transferred into trout. Regardless of the fact that rGLO transcription occurred in embryos, neither GLO protein, nor enzyme activity were detected. There was no production of L-AA in transgenic fish raised on vitamin C-free diets or injected with L-gulonolactone. These results indicated that the conditions required for translation or stability of rGLO were not present in trout tissues. To augment carbohydrates utilization, human glucose transporter 1 and rat hexokinase II cDNAs were tested. In the transfected embryos. HK activity, rates of hexose uptake and glucose oxidation were increased. The effect of hGLUT1 on glucose metabolism was greater than that of rHKII. Trout carrying hGLUT1 and rHKII with viral or piscine promoters were created. Though interpretation of the metabolic effects of the transgenes was complicated with mosaicism, a tendency to improved carbohydrate utilization was revealed in some of the transgenic individuals.

Uptake of 99mTc(5+)-complexes in ischemic myocardial slices and their dissociable ability

AIM

To find how some technetium-complexes to deliver the active species, TcO4(3-), to the target tissue from a dissociable polynuclear Tc5+ species in preserved states in vivo.

METHODS

Effect of dissociation ability of the polynuclear Tc5+ complexes on their accumulation in ischemic myocardium was tested. Ability of dissociation as having an appropriate conformation to become biologically functional after entering the blood circulation was tested using a simple dilution method by thin layer chromatography (TLC) analysis. Various degree of ischemic myocardium slices of rat were incubated with 1/100 diluted 99mTc(5+)-succimer, 99mTc(5+)-GH and 99mTc(5+)-PPi.

RESULTS

The TLC patterns of 99mTc(5+)-GH and 99mTc(5+)-PPi showed the presence of a fast increasing of free Tc-species as dilution degree increased. The relative radioactivity of peak of free pertechnetate (Rf = 0.85-1.0) with 1:500 dilution was: 99mTc(5+)-succimer 0%, 99mTc(5+)-GH 28.1% +/- 1.3%, and 99mTc(5+)-PPi 46.0% +/- 2.9% respectively. The uptake of the myocardium after ischemia for 3 h was 99mTc(5+)-succimer 420% +/- 110% dose/g tissue, 99mTc(5+)-GH 710% +/- 180% dose/g tissue, and 99mTc(5+)-PPi 1295% +/- 390% dose/g tissue respectively.

CONCLUSION

The dissociation and myocardial uptake showed: 99mTc(5+)-succimer < 99mTc(5+)-GH < 99mTc(5+)-PPi, the uptake by the ischemic myocardium is positively correlated to their dissociation.

Novel 99mTc aminobisthiolato/monothiolato "3 + 1" mixed ligand complexes: structure-activity relationships and preliminary in vivo validation as brain blood flow imaging agents

A series of neutral, lipophilic 99mTc mixed-ligand complexes of the general formula 99mTcOL1L2, where L1H2 is an N-substituted bis-(2-mercaptoethyl)amine, [X-CH2CH2N(CH2CH2SH)2], [SNS], and L2H is a monodentate thiol (RSH), [S], has been synthesized and evaluated in rodents for potential use in brain blood flow imaging. The complexes were prepared by ligand exchange reaction using 99mTc(V)O-glucoheptonate as precursor and equimolar quantities of the two ligands. In all cases the syn isomer was formed in a high yield, whereas the anti isomer was not always present. The formation of two isomeric complexes-syn and anti-was expected, since the N-substituent (X-CH2CH2N) can assume syn or anti configuration with respect to the 99mTcO3+ core during complexation. One anti and all syn isomers were isolated by HPLC. Their identity was confirmed by comparative HPLC studies with the analogous 99Tc complexes of established structure. In vivo distribution, in particular brain uptake and retention, greatly depended on the type of either tridentate (L1H2) or monodentate (L2H) ligand. All 99mTc complexes showed significant brain uptake in mice (0.78-4.35% injected dose per organ at 5 min postinjection). This initial uptake remained nearly constant for at least 30 min for most of the complexes. Structure-activity relationships of novel 99mTc(V)O SNS/S complexes in mice are reported and discussed. Selected complexes were further studied in rats. High brain uptake, comparable to that of 99mTc-d,l-HMPAO, and sufficient retention 60 min postinjection were provided with complex 18 [X = (C2H5)2N and R = p-CH3OC6H4CH2].

A comparison of cleavable and noncleavable hydrazinopyridine linkers for the 99mTc labeling of Fab' monoclonal antibody fragments

The design and synthesis of hydrazinopyridine bifunctional chelating agents (BCA's) featuring amide, ester, and disulfide groups are described. The BCA's site-specifically react with the free thiol groups of the tumor-specific monoclonal antibody fragment C46.3 using a one-pot in situ reduction and conjugation procedure from the F(ab')2 to give Fab'-linker conjugates. Molar substitution ratios (MSR's) of the hydrazinopyridine conjugates were comparable to the theoretical (maximum) number of thiols per fragment determined by free hydrazine and residual thiol assays. The series of C46.3 Fab'-linker conjugates were 99mTc-labeled in greater than 95% radiochemical purity by incubation with 99mTc-tricine for 1 h at room temperature. In order to evaluate the conjugates for radiopharmaceutical applications, the tumor localization and biodistribution properties of the radiolabeled Fab'-linker conjugates, compared to the direct labeled fragment, were tested in nude mice bearing LS174T xenografts. Depending upon the structure of the linker connecting the radiolabeled hydrazinopyridine group to the antibody fragment, we observed a variation in kidney uptake and whole-body clearance. Diester- and monoester-linked conjugates exhibited lower kidney uptake and faster whole-body clearance than the corresponding linker containing amide groups. This result may be interpreted as evidence for rapid metabolism of ester compared to amide groups in the kidney following uptake. At 24-h postinjection, the monoester-linked conjugate 99mTc-C46.3 Fab'-BA displayed the highest tumor: blood ratio (16.2) compared to the directly labeled conjugate (6.6) and is therefore a potential clinical candidate for imaging breast and ovarian cancer.

99Tcm-cystine, a renal function and imaging agent: a comparative study in dog with 131I-hippurate and 99Tcm-glucoheptonate to evaluate its functional and imaging characteristics

99Tcm-cystine, which has been proposed as a renal radiopharmaceutical for evaluating renal morphology and function in a single experiment, is compared with 131I-orthoiodohippurate (OIH) with respect to its renal clearance and extraction parameters and with 99Tcm-glucoheptonate (GHA) regarding its imaging characteristics. In spite of its comparable renal accumulation with 131I-OIH, its clearance (10.1 +/- 1.0 ml min-1 kg-1) was lower than that of 131I-OIH (21.5 +/- 0.9 ml min-1 kg-1) but was higher than that of 125I-iothalamate (5.4 +/- 0.6 ml min-1 kg-1). Extraction efficiencies of 99Tcm-cystine, 131I-OIH and 125I-iothalamate were 39 +/- 5, 64 +/- 4 and 27 +/- 3, respectively. The glomerular filtration components of 99Tcm-cystine and 131I-OIH were 26 and 16% of their respective clearances. In probenecid-treated animals the clearance of both agents was affected to a similar extent and fell to half of their respective control values, whereas tubular secretory components were found to be 19 and 31% of the controls. The kidney images obtained with 99Tcm-cystine were superior to those obtained with 99Tcm-GHA at different time points. Therefore, considering both renal function and imaging properties of 99Tcm-cystine it appears that this radiopharmaceutical offers some definite advantages over the currently available renal agents and commands further study.

Evaluation of sterically stabilized liposomes as a vehicle for targeting technetium-99m labelled radiopharmaceuticals

Sterically stabilized neutral liposomes (multilamellar vesicles) were prepared by sonicating phosphatidylcholine and cholesterol (molar ratio 4:1) film in phosphate buffered saline (50 mM, pH 7.4) containing 4% Tween 20. Tc-99m-GHA was incorporated in these liposomes by treating 0.5 ml of the suspension with lyophilized GHA kit (5 mg GHA and 250 micrograms SnCl2 x 2 H2O) followed by addition of 1 ml 99mTcO4- (1-3 mCi). The labelling yield was 60-70%. Tween 20 has provided significant stability of the radiolabel as compared to that without its addition, when radiolabelled liposomes were incubated in serum up to 24 h. With respect to Tc-99m-GHA alone, radiolabelled liposomes exhibited 4- to 6-fold greater radioactivity in the blood of rabbits (15 min-24 h). Comparison of biodistribution data of radiolabelled liposomes and Tc-99m-GHA in mice demonstrated a 10- to 12-fold greater hepatic accumulation of radiolabelled liposomes with respect to that of Tc-99m-GHA throughout the period of study (15 min-24 h), though their concentration in the kidneys was comparable.

The effect of captopril on glucoheptonate uptake in experimental renal artery stenosis

This study attempted to evaluate the role of glucoheptonate (GHA) in captopril renography in an in vivo laboratory investigation in which postcaptopril glucoheptonate uptake was analysed in awake 2KlC hypertensive rats. Clamped kidney uptake in a previous study was greater in the poststenotic kidney than in the normal kidney (P = 0.01) in rats with mild renal artery stenosis. A glucoheptonate renogram protocol was developed for use in rats anaesthetized with sodium pentobarbital. An 123I-hippuran scan was performed to determine the relative renal function, followed by a control 99Tcm-GHA scan. Five minutes after administering captopril, another 99Tcm-GHA scan was performed. Relative renal uptake was determined between 30 and 90 s postinjection. 99Tcm-GHA uptake in the clamped kidney was more than 50% of total uptake in 3/9 of the abnormal rats' control scans. No abnormal rats clamped kidney 99Tcm-GHA uptake was greater than 50% in the postcaptopril scans. Captopril reduced GHA uptake in all nine of the animals with baseline scans. These findings suggest that the laboratory observation of captopril induced paradoxically increased 99Tcm-GHA uptake in renal artery stenosis may not be observed scintirenographically. Moreover, the data support a potential value of glucoheptonate in captopril renography.

The effects of anesthesia on osmotic blood-brain barrier disruption

To evaluate the effect of various anesthetic agents on hyperosmolar blood-brain barrier disruption (BBBD), Sprague-Dawley rats were given pentobarbital (PB), ketamine-xylazine (KX), isoflurane (IF), methoxyflurane (MF), or fentanyl-droperidol (FD) before intracarotid infusion of mannitol or saline. Physiological monitoring showed that the effects of mannitol infusion differed significantly from those of saline infusion and were associated with transient bradycardia, hypotension, metabolic acidosis, and electroencephalographic depression. With PB, KX, or IF anesthesia, we obtained excellent BBBD as evidence by 3+ Evans blue staining of the mannitol-infused cerebral hemisphere. FD anesthesia was associated with tachycardia and MF anesthesia resulted in hypotension; both showed poor Evans blue staining. Radioisotope delivery to the disrupted hemisphere averaged 0.80% of the administered 125I-albumin compared to 0.03% in the contralateral and 0.06% in control (saline-infused) hemispheres. 99mTc-glucoheptonate delivery measured 0.49% of the administered dose after BBBD, 0.03% contralaterally, and 0.05% in control hemispheres. Pharmacological manipulation to normalize the cardiac index in the FD and MF groups resulted in 3+ Evans blue staining and significantly increased delivery of albumin and glucoheptonate. This study suggests that the cardiovascular changes of these specific anesthetic agents are important in obtaining optimal hyperosmolar BBBD.

Permeability of blood vessels in experimental gliomas: uptake of 99mTc-glucoheptonate and alteration in blood-brain barrier as determined by cytochemistry and electron microscopy

Experimental gliomas were induced in rats by prenatal exposure to ethyl nitrosourea. Changes in the blood-brain barrier were determined by the uptake of a water-soluble compound, 99mTc-glucoheptonate. Increased uptake of 99mTc-glucoheptonate was measured in intact tumors and in various sectors of dissected tumors. The extent of 99mTc-glucoheptonate uptake greatly varied among different tumors and among different sectors of the same tumor. Ultrastructural and cytochemical analysis of the capillary endothelial wall revealed major alterations in tight junctions, which became permeable to horseradish peroxidase. In brain tissue around the tumors, uptake of 99mTc-glucoheptonate and ultrastructure of tight junctions were comparable to normal brain capillaries. The results of the present study indicate that altered endothelial tight junctions may provide the main route of transport of 99mTc-glucoheptonate through the endothelial wall.

SPECT quantitation of cobalt-57 bleomycin delivery to human brain tumors

A newly developed and validated noninvasive quantitative SPECT method was used to measure the in vivo uptake of [57Co]bleomycin (Co-bleo) in 13 human brain tumors and the uptake of [99mTc]glucoheptonate (GH) in 23 brain tumors. Significant differences in tumor uptake were found. The tumor concentration over time, the tumor to blood radio at 30 min and the tumor cumulative concentration of radioactivity showed marked differences even between tumors with the same histology. Only a weak correlation was found between tumor concentration of Co-bleo and of GH. Therefore a simple imaging agent such as GH cannot, at the present time, serve as an indicator of individual tumor uptake and further experience with other agents is still necessary. Contrary to the generally held view, no correlation was found between the concentration of drug in the blood and its tumor concentration. It is suggested therefore that the level of a drug in the blood cannot be used as a criterion of the amount that will penetrate the tumor. Direct SPECT measurement of the concentration of the drug in the tumor itself should be performed. The bioavailability of a drug is critical in order for it to exert it tumoricidal effect. The results, showing marked differences in uptake between brain tumors, suggest that before chemotherapy is administered, uptake of the chemotherapeutic drug in the individual tumor to be treated should be assessed and comparisons should be made between the uptake of a series of drugs to determine which drug would be most efficacious on the basis of its uptake as well as its tumor cell killing potential.

Breast milk radioactivity following injection of 99Tcm-pertechnetate and 99Tcm-glucoheptonate

Measurements were made of the concentration of radioactivity in the breast milk of two patients: one following 100 MBq (2.7 mCi) 99Tcm-pertechnetate administration, and the other following administration of 550 MBq (15 mCi) 99Tcm-glucoheptonate. The fractional activity concentrations in the former case were about two orders of magnitude greater than in the latter and the effective half lives of secretion were 3 and 4 h, respectively. An infant breast fed without interruption would have ingested 5.2 and 0.055% of the 99Tcm administered with pertechnetate and with glucoheptonate, respectively. The former fractional ingestion was compatible with the larger value expected following pertechnetate injection without perchlorate pretreatment, and would have produced an effective dose equivalent to the infant of 1.5 mSV. An interruption to feeding of 12 h would reduce this dose to 0.2 mSV. It was concluded that breast feeding need not be interrupted after injection of 99Tcm-glucoheptonate other than for a short period of reassurance.