Thakuri Singh

Scintigraphic diagnosis of protein losing enteropathy using Tc-99m dextran.

The authors performed abdominal scintigraphy using intravenously administered Tc-99m dextran in a patient with protein losing enteropathy. The study revealed abnormal leakage of the radiotracer in the left lumber area that moved over time in a pattern suggestive of small intestinal transit. Besides being a nonprotein and having long stay in intravascular compartment, the macromolecule may have many advantages over Tc-99m human serum albumin, the current radiotracer of choice for imaging intestinal protein loss.

Technetium-99m dextran: a promising new protein-losing enteropathy imaging agent

The purpose of this study was to evaluate technetium-99m dextran (99mTc-Dx; molecular weight 81000) as a prospective protein-losing enteropathy (PLE) imaging agent. Twenty-two patients with diseases commonly associated with PLE and 12 healthy control subjects underwent intravenous99mTc-Dx scintigraphy. All of the 22 test patients showed significant radiotracer accumulation in the intestines within 3–4 h post injection. The focal, regional or generalised nature of the enteropathy and involvement of the large or small intestine could be identified in most cases. Four of the 12 apparently healthy subjects also showed minimal accumulation in the abdominal area occurring late in the study period. This could have been physiological, related to food habits or due to unsuspected intestinal worms. We attribute the high sensitivity of99mTc-Dx to its relatively fast blood (background) clearance. The radiotracer may have several other advantages over99mTc-labelled human serum albumin in imaging PLE.

Radiolabeling and dose fixation study of oral alpha-ketoglutarate as a cyanide antidote in healthy human volunteers

Context. Radiolabeling and dose fixation study of alpha-ketoglutarate (A-KG). Objective. A-KG is a potential oral antidote for cyanide poisoning. Its protective efficacy in animals was best exhibited at a dose of 2.0 g/kg body weight, which when extrapolated to human is very high. The objective of this study was to reduce the dose of A-KG in humans with concomitant increase in its bioavailability, employing pharmacoscintigraphic techniques to assess kinetics in man. Materials and methods. A-KG was radiolabeled with technetium-99m pertechnetate (Tc-99m) and its purity, labeling efficiency, and stability in vitro were determined by instant thin layer chromatography. Time-dependent bio-absorption of the drug in rats and rabbits was assessed by gamma scintigraphy after oral administration of a tracer dose of 99mTc-A-KG mixed with nonradioactive A-KG at a concentration of 0.1–2.0 g/kg in the presence or absence of aqueous dilution. Furthermore, scintigraphy and radiometry studies were performed in healthy human volunteers using 5–20 g of A-KG, given in single or split doses followed by different quantity of water. Drug bioavailability was estimated periodically. Results. High radiolabeling (>97%) of A-KG with a stability of 24 h in vitro was obtained. Less than 1% absorption of the drug occurred within 20 min after A-KG was administered in animals at a concentration of 2.0 g/kg body weight. One-tenth reduction in dose increased the bioavailability to 15%. Significant improvement in gastric emptying of the drug was achieved when the drug was administered along with 1–5 mL of water. In humans, two doses of 10 g A-KG given at an interval of 10 min, followed by 300 mL of water, increased the drug bioavailability to 40% as compared to a single dose of 20 g. Discussion. Significant reduction in A-KG dose was achieved in humans as compared to the recommended dose in animals. Conclusion. Aqueous dilution improves the bioavailability of A-KG in humans.

Tc-99m dextran: a new and sensitive general purpose scintigraphic agent for diagnosing intestinal inflammation.

PURPOSE This feasibility study was undertaken to compare the sensitivity of Tc-99m dextran with that of Tc-99m human immunoglobulin G to diagnose ulcerative colitis, and to explore its possible role in disease follow-up. MATERIALS AND METHODS Twenty-six patients with active disease and six patients in remission underwent serial Tc-99m dextran scanning for as long as 3 hours or more after injection. Eight of the patients with active disease also underwent Tc-99m human immunoglobulin G imaging. RESULTS Twenty-four of 26 (92%) patients with active ulcerative colitis had a positive result of the Tc-99m dextran study, mainly within 1 hour. In comparison, Tc-99m human immunoglobulin G accumulated abnormally in four of eight (50%) patients and had a relatively poor target localization with high persisting background even after 6 hours. Four of the six patients in remission still had a positive result of the dextran scan, but the abnormal uptake was less than that in the patients with active disease. The disease has recurred already in one of these patients. A patient with pancolitis who was receiving steroid enema therapy had intense uptake of Tc-99m dextran in the ascending colon, probability because it was outside the range of the enema. CONCLUSIONS Tc-99m dextran is a sensitive and cost-effective agent to diagnose ulcerative colitis, and it may have a role in disease follow-up.

Inflammation imaging using Tc-99m dextran

Tc-99m dextran has been shown to have inflammation imaging capability. Two cases are presented: one with Meckels diverticulum and another with osteomyelitis. In both, the agent correctly identified the abnormal sites. It appeared to be better than Tc-99m pertechnetate and Tc-99m MDP in these conditions. Its nonprotein nature, easy and stable tagging, and good target-to-nontarget ratio make it a practical inflammation imaging radiotracer.

A new method for radiolabeling of human immunoglobulin-G and its biological evaluation.

Background: Radiolabeled human Immunoglobulin-G (hIgG) has demonstrated its utility in inflammation and infection imaging. However, the present method of radiolabeling hIgG is time-consuming and complex. Objective: To develop a simplified method of radiolabeling hIgG with technetium-99m (99mTc) via a nicotinyl hydrazine derivative (99mTc-HYNIC-hIgG) and its biological evaluation. Results: In vitro and in vivo studies showed that 99mTc-hIgG prepared by this method was fairly stable in physiological saline and human serum till 24 h. Only 4.3% degradation of the radiolabeled drug was seen till 24 h. Blood clearance pattern of the radiopharmaceutical exhibited biphasic exponential pattern. Biodistribution of 99mTc-HYNIC-hIgG in mice was observed up to 24 h. Significant accumulation of the radiotracer was found in liver (4.93 %), kidney (3.67%) and intestine (2.12 %) at 4 h interval by 24 h interval, it was reduced to 1.99%, 2.18% and 1.93 % respectively. Significant amount of radioactivity in liver, kidney and intestine suggest hepatobilliary as well as renal route of clearance for 99mTc-HYNIC-hIgG. The anterior whole body and spot scintigraphy images showed increased uptake of 99mTc-HYNIC-hIgG, with the area seen as a focal hot spot, indicating good localization of the radiolabeled hIgG at the site of infection. Conclusion: The present findings indicate that 99mTc-HYNIC-hIgG holds great potential for the scintigraphy localization of inflammation. The shelf life of the developed kit, when stored at (–) 20°C was found to be at least 3 months.

Development of nano alpha-ketoglutarate nebulization formulation and its pharmacokinetic and safety evaluation in healthy human volunteers for cyanide poisoning

Development of nano alpha-ketoglutarate (A-KG) nebulization formulation for neutralization of inhaled cyanide ion toxicity. Objectives of the present study were to (a) develop a novel A-KG nebulization formulation against cyanide poisoning, particularly hydrogen cyanide gas (b) validate its respiratory fraction in vitro and in vivo, and (c) create its pharmacokinetic data in human volunteers. The formulation was optimized on the basis of particle size of aerosolized droplets after nebulization in 6 volunteers. Gamma scintigraphy was used to quantify total and regional lung deposition of nebulized A-KG after radiolabeling it with Technetium-99m. The formulation was optimized using 30% ethanol-saline with particle size in the range of 300-500 nm. In vitro and in vivo studies showed that drug nebulization resulted in a significant respirable fraction of 65 ± 0.6% with whole lung deposition of 13 ± 1%. Human pharmacokinetic data was derived in 6 healthy human volunteers with peak serum concentration (C(max)) of 39 ± 3 μg/ml, while the area under curve (AUC) after inhalation was 376 ± 23 μg × h/ml indicating that the drug was rapidly and completely absorbed when targeted directly to lungs. Significant lung deposition of A-KG was achieved with the developed formulation. The formulation appears to have several advantages, including the potential of neutralizing inhaled CN(-) ions in the lungs themselves. It is a safe and efficacious procedure, suitable for hospital or ambulance use in accidental cyanide poisoning cases, or as a preventive approach for fire-rescue teams.

Nose to Brain Delivery of Midazolam Loaded PLGA Nanoparticles: In Vitro and In Vivo Investigations.

OBJECTIVES The present study is aimed to develop poly(D, L-lactide-co-glycolic acid) (PLGA) nanoparticles (NP) loaded with midazolam (Mdz) for nose to brain delivery. MATERIALS AND METHODS NP were formulated by nanoprecipitation and characterized for z-average, zeta potential, % drug entrapment and ex vivo drug release. Mdz NP (MNP) were radiolabeled with technetium-99m. Biodistribution and gamma scintigraphic studies were performed on Sprague-Dawley rats following intranasal (i.n) and intravenous (i.v) administration to trace the transport of Mdz for nose-to-brain delivery. RESULTS AND DISCUSSION MNP showed z-average of 164±4.5nm with polydispersity index 0.099±0.02 and zeta potential of -16.6±2.5mV. Ex vivo drug studies indicated that MNP showed 29±1.2% of permeation upto 4h via sheep nasal mucosa, whereas Mdz suspension (MS) showed drug release of 83±1.2% within 4h. Comparing i.n administration of MNP, MS and i.v administration of MS, scintigraphy imaging and Brain/blood uptake ratios indicated higher brain targeting via i.n administration of MNP. CONCLUSION Results indicated that the i.n MNP could be employed as a non invasive mode of delivery system with improved drug entrapment, stability and controlled drug release over a period of time.

Biodistribution and scintigraphic evaluation of 99mTc-Mannan complex

Technetium-99m (99mTc) is extensively used in nuclear medicine, mostly used to label radiopharmaceuticals and in radio diagnostics. In the present study, we directly radiolabeled mannan with 99mTc by using Tin(II) Chloride Dihydrate (SnCl2·2H2O) as a reducing agent. Mannan, a TLR agonist is a complex carbohydrate identified as a potential modulator of biological effects of ionizing radiation, both in vitro and in vivo, in our laboratory. Under in vivo conditions mannan modulates radiation response when administered through either oral or parenteral routes. The present study aims to understand the pharmacologic biodistribution of the 99mTc-mannan complex in mice (via oral, i.p. and i.v. routes) using non-invasive scintigraphic imaging and invasive radiometry. Qualitative and quantitative analysis of 99mTc-mannan complex was performed by ITLC-SG, ascending paper chromatography. Radio-complexation efficiency of >98% was consistently achieved with hydrolyzed reduced Tc-99m being 1-2%. We confirmed stability of complex in saline and serum up to 24 h at room temperature. Biodistribution studies were performed using the above radiocomplex in BALB/c mice and 99mTc-mannan complex was administered though oral, i.p. and i.v. routes. To our expectations, most of the radioactivity accumulated in stomach and small intestine in mice with oral administration, along with insignificant activity in the remaining studied organs. It suggests that 99mTc-mannan complex did not get absorbed from the gut and was removed as such in the fecal material. On the contrary, i.p. and i.v administration of mannan resulted in significant accumulation of the 99mTc-mannan complex in kidney, liver, intestine, lungs, spleen, bone marrow, blood and heart, at both 1 h and 4 h after i.v. administration. The remaining organs (stomach, testis and muscles) showed lower accumulation of the 99mTc-mannan complex. 99mTc-mannan complex was adminstered (i.v.) in New Zealand white rabbits and it was evident from the scintigraphic images that mannan cleared very rapidly from the administration site and reached into systemic circulation. No activity in the thyroid, salivary gland, or gastric mucosa suggests an insignificant amount of free pertechnetate in the 99mTc-complex preparation, further confirming the in vivo stability of the radiolabeled mannan complex. Significant amount of radioactivity in liver, intestine and kidneys suggests hepatobiliary as well as renal routes of clearance. The bio-availability of the complex varies with the route of administration. An entirely different biodistribution pattern exists when the same molecule is administered through oral or parenteral route. Our study is the first step towards a better understanding of the mechanisms involved in radiation modulation offered by mannan administration, in vivo.

Development and validation of hydroxy ethyl starch kits for instant use in gastroesophageal reflux and gastric motility studies

A reduction method based on stannous chloride is described to prepare hydroxy ethyl starch kits for gastrointestinal reflux and gastric motility studies. Following verification of the consistency of radiolabelling, in vitro experiments were carried out to validate 99mTc hydroxy ethyl starch as a liquid phase and solid phase gastric motility imaging radiotracer. Gastroesophageal reflux, liquid phase and solid phase studies were then conducted in 13 adult volunteers to examine the in vivo stability of the radiotracer. High labelling efficiency (>95% when prepared at neutral pH) was consistently achieved, which remained stable in conditions simulating gastric environment. Twelve of the 13 volunteers did not show absorption of any radioactivity from the gastro-intestinal tract. 99mTc hydroxy ethyl starch is a new agent suitable for gastroesophageal reflux and gastric motility studies. It is available in kit form and is a more ‘physiological’ agent than 99mTc sulphur colloid for preparing a solid radioactive meal. 99mTc hydroxy ethyl starch represents a true carbohydrate meal, and unlike 99mTc sulphur colloid, is easy to prepare and can easily be standardized to produce a standard vegetarian meal.