Vector-mediated delivery of a polyamide ("peptide") nucleic acid analogue through the blood-brain barrier in vivo

Polyamide ("peptide") nucleic acids (PNAs) are molecules with antigene and antisense effects that may prove to be effective neuropharmaceuticals if these molecules are enabled to undergo transport through the brain capillary endothelial wall, which makes up the blood-brain barrier in vivo. The model PNA used in the present studies is an 18-mer that is antisense to the rev gene of human immunodeficiency virus type 1 and is biotinylated at the amino terminus and iodinated at a tyrosine residue near the carboxyl terminus. The biotinylated PNA was linked to a conjugate of streptavidin (SA) and the OX26 murine monoclonal antibody to the rat transferrin receptor. The blood-brain barrier is endowed with high transferrin receptor concentrations, enabling the OX26-SA conjugate to deliver the biotinylated PNA to the brain. Although the brain uptake of the free PNA was negligible following intravenous administration, the brain uptake of the PNA was increased at least 28-fold when the PNA was bound to the OX26-SA vector. The brain uptake of the PNA bound to the OX26-SA vector was 0.1% of the injected dose per gram of brain at 60 min after an intravenous injection, approximating the brain uptake of intravenously injected morphine. The PNA bound to the OX26-SA vector retained the ability to bind to synthetic rev mRNA as shown by RNase protection assays. In summary, the present studies show that while the transport of PNAs across the blood-brain barrier is negligible, delivery of these potential neuropharmaceutical drugs to the brain may be achieved by coupling them to vector-mediated peptide-drug delivery systems.

Human insulin receptor monoclonal antibody undergoes high affinity binding to human brain capillaries in vitro and rapid transcytosis through the blood-brain barrier in vivo in the primate

PURPOSE

The ability of monoclonal antibodies against the human insulin receptor to undergo transcytosis through the blood-brain barrier (BBB) was examined in the present studies.

METHODS

Two murine monoclonal antibodies (MAb83-7 and MAb83-14) which bind different epitopes within the alpha-subunit of the human insulin receptor were examined using isolated human brain capillaries, frozen sections of primate brain, and in vivo pharmacokinetic studies in anesthetized Rhesus monkeys.

RESULTS

Both antibodies strongly illuminated capillary endothelium in immunocytochemical analysis of frozen sections of brain from Rhesus monkey but not squirrel monkey. Both monoclonal antibodies, in the iodinated forms, bound to human brain microvessels, although the binding and endocytosis of MAb83-14 was approximately 10-fold greater than MAb83-7. The active binding of MAb83-14 to the human insulin receptor was paralleled by a very high rate of transport of this antibody through the BBB in vivo in two anesthetized Rhesus monkeys. The BBB permeability-surface area (PS) product in neocortical gray matter was 5.4 +/- 0.6 microL/min/g, which is severalfold greater than previous estimates of the PS product for receptor-specific monoclonal antibody transport through the BBB. The brain delivery of MAb83-14 to the Rhesus monkey brain was high and 3.8 +/- 0.4% of the injected dose was delivered to 100 g of brain at 3 hours after a single intravenous injection. In contrast, there was no brain uptake of the mouse IgG2a isotype control antibody.

CONCLUSIONS

These studies demonstrate an unexpected high degree of transcytosis of a monoclonal antibody through the primate BBB in vivo.

Transferrin-antibody fusion proteins are effective in brain targeting

In the present study, the receptor binding potential of transferrin (Tf) was linked to an antibody binding specificity. Human Tf was fused to mouse-human chimeric IgG3 at three positions: at the end of heavy chain constant region 1 (CH1), after the hinge, and after CH3. The resulting Tf-antibody fusion proteins were able to bind antigen and the Tf receptor. The CH3-Tf fusion protein showed no complement-mediated cytolysis but possessed IgG receptor I (Fc gamma RI) binding activity. Most importantly, all of the fusion proteins demonstrated significant uptake into brain parenchyma, with 0.3% of the injected dose of the hinge-Tf fusion protein rapidly targeted to the brain. Recovery of iodinated CH3-Tf fusion protein from the brain parenchyma demonstrated that the fusion proteins can cross the blood-brain barrier intact. The binding specificity of these fusion proteins can be used for brain delivery of noncovalently bound ligands, such as drugs and peptides, or for targeting antigens present within the brain.

In vivo cleavability of a disulfide-based chimeric opioid peptide in rat brain

Brain delivery of systemically administered neuropeptide drugs may be achieved by the synthesis of chimeric peptides, wherein the peptide is coupled to transport vectors via avidin-biotin technology. The present study focuses on factors that optimize the linkage of drugs to transport vectors. The vector is the OX26 monoclonal antibody to the transferrin receptor, and the model peptide used in these studies is [Lys7]dermorphin (K7DA). The K7DA is monobiotinylated at the epsilon-amino group of the Lys7 residue with either a cleavable linker, e.g., disulfide, using NHS-SS-biotin, or a noncleavable linker, e.g., amide, using NHS-XX-biotin. Disulfide cleavage of the biotinylated derivative yields the desbiotinylated peptide, which is thiolated. Structures of the K7DA analogues were confirmed by secondary ion mass spectrometry. The biotinylated peptides were coupled to a thiol-ether conjugate of the OX26 antibody and either neutral avidin (NLA) or streptavidin. The binding constants (Ki) of the K7DA, the biotinylated K7DA (bio-XX-K7DA), the desbiotinylated K7DA, and the bio-XX-KD7A conjugated to NLA-OX26 were 0.62 +/- 0.14, 1.59 +/- 0.27, 1.24 +/- 0.24, and > 10 nM, respectively, and were determined with a mu-opioid peptide radioreceptor assay. Comparable results were obtained with in vivo tail-flick analgesia testing following intracerebroventricular (icv) injection of opioid chimeric peptides. Reversibility of pharmacologic action of thiolated peptide was demonstrated by icv naloxone administration. The cleavability of the disulfide linker in vivo in rat plasma and brain was assessed with gel filtration HPLC and internal carotid artery perfusion of labeled opioid chimeric peptides.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics and organ clearance of a 3'-biotinylated, internally [32P]-labeled phosphodiester oligodeoxynucleotide coupled to a neutral avidin/monoclonal antibody conjugate

The pharmacokinetics and organ uptake of a 3'-biotinylated, [32P] internally labeled 36-mer phosphodiester oligodeoxynucleotide (PO-ODN) were measured after intravenous injection in the anesthetized adult rat. The PO-ODN was antisense to the tat gene of the human immunodeficiency virus, and was 3'-biotinylated to a) protect against serum and tissue 3'-exonuclease activity, and b) facilitate coupling to a neutral avidin-based transcellular drug delivery vector. The latter was comprised of a covalent conjugate of neutral avidin (NLA) and the OX26 murine monoclonal antibody to the rat transferrin receptor. The PO-ODN was internally labeled at the 21-nucleotide position to prevent rapid hydrolysis [32P] label by serum and tissue 5'-phosphatases. The uptake of the 3'-bio-[32P21]PO-ODN by brain, heart, kidney, lung, and liver was measured. The studies show that the unconjugated 3'-bio-[32P21]PO-ODN was rapidly removed from plasma, with a mean residence time of 22 +/- 1 min and a systemic clearance of 9.2 +/- 0.5 ml/min/kg. Large amounts of [32P] radioactivity were recovered in the urine following the injection of the PO-ODN, and when this fraction was included in the calculation of the renal clearance parameter, the renal clearance was 20-fold higher, indicating the principal site of organ clearance of the unconjugated PO-ODN was the kidney. Conjugation of the 3'-bio-PO-ODN to the NLA-OX26 vector reduced the systemic clearance 50%, owing to a > 10-fold reduction in renal clearance. Following conjugation of the 3'-bio-PO-ODN to the NLA-OX26 vector, the major clearance organ was the liver.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics of [3H]biotin bound to different avidin analogues

The use of avidin-biotin technology in drug delivery facilitates the conjugation of biotinylated therapeutics to transport vectors that are enabled to undergo receptor-mediated transcytosis through the brain capillary endothelial wall, which makes up the blood-brain barrier (BBB) in vivo. However, the conjugation of avidin, a cationic glycosylated protein, to transport vectors greatly increases the rate of removal of the vector from the bloodstream, owing to rapid uptake of avidin by peripheral tissues such as liver and kidney. However, modified avidins may retain high affinity biotin binding properties, but may not be rapidly removed from plasma by peripheral tissues, and such avidin analogues would provide preferred plasma pharmacokinetic profiles. Therefore, the present studies investigate the pharmacokinetics of plasma removal of [3H]biotin bound to one of six different avidin analogues: streptavidin, Neutra-lite avidin, avidin, neutral avidin, Lite-avidin, and succinylated avidin. Isoelectric focusing studies show that avidin and Lite-avidin were highly cationic proteins, whereas neutral avidin, Neutra-lite avidin, and streptavidin were neutral proteins, and succinylated avidin had an acidic isoelectric point. The avidin analogues fell into two groups with respect to rate of biotin removal from plasma. The low clearance group included streptavidin and Neutra-lite avidin, which had a mean plasma clearance of 0.41 mL/min/kg. The high clearance group consisted of succinylated avidin, neutral avidin, and Lite-avidin and had a mean plasma clearance of 17 mL/min/kg, or 40-fold faster than the low clearance avidins.(ABSTRACT TRUNCATED AT 250 WORDS)

Solitary rectal ulcer and complete rectal prolapse: one condition or two?

We studied the physiological features of patients with complete rectal prolapse and different degrees of solitary rectal ulcer syndrome to determine whether these conditions are likely to form part of the same disorder. 52 solitary rectal ulcer patients (median age 31, 40 females), and 15 complete rectal prolapse patients (median age 31, 12 females) were studied. Solitary rectal ulcer patients were divided into 3 groups, based on the extent of accompanying rectal prolapse (no prolapse, internal prolapse, or external prolapse). Both solitary rectal ulcer patients without prolapse and with internal prolapse had significantly higher maximum anal resting (p < 0.01 for both groups) and squeeze pressure (p < 0.05 for both groups) than complete rectal prolapse patients. In contrast, solitary rectal ulcer patients having external prolapse were similar to those with complete rectal prolapse. Solitary rectal ulcer patients without rectal prolapse had significantly decreased anal and rectal electrosensitivity (p < 0.01 for both) when compared to healthy control subjects. Solitary rectal ulcer patients therefore have a spectrum of clinical and physiological features--this condition may comprise a range of different disease entities. The findings also suggest a different underlying aetiopathophysiology of solitary rectal ulcer from that of complete rectal prolapse.

Loss of heterozygosity on the short arm of chromosome 17 in uterine cervical carcinomas

DNA samples from 26 cervical carcinoma and normal tissue pairs were studied by restriction fragment length polymorphism (RFLP) analysis to determine the frequency of loss of heterozygosity (LOH) on 17p. Allelic loss in the p13.1 region of chromosome 17, known to contain the TP53 locus, was not detected in any of 10 informative cases. Instead, LOH was detected on 17p13.3 in eight (40%) of 20 informative cases with at least one of two 17p13.3 markers. Examination of the intragenic region of p53 in the same samples using polymerase chain reaction (PCR)-RFLP analysis showed no LOH in the gene (none of 16 informative individuals).

In vivo demonstration of subcellular localization of anti-transferrin receptor monoclonal antibody-colloidal gold conjugate in brain capillary endothelium

To study transcytosis at the blood-brain barrier (BBB) in vivo, we used the internal carotid artery perfusion technique in rats. Brain uptake of the OX26 anti-transferrin receptor antibody (IgG2a) coupled to 5-nm colloidal gold (OX26-Au) was morphologically examined after infusion or perfusion into the carotid artery for 10 min. The brain tissue was subsequently perfusion-fixed with 2% glutaraldehyde. By light microscopy, silver enhancement of vibratome sections revealed staining of the vascular tree. Electron microscopy showed binding of gold particles at the luminal plasma membrane of brain capillary endothelia, endocytosis in vesicles (50-100 nm), and particles beyond the abluminal plasma membrane. Studies were performed with an IgG2a isotype control, UPC10. Internal carotid artery infusion of [125I]-UPC10 showed no evidence of brain uptake or binding to endothelium. However, microvessel structures were identified after silver enhancement of vibratome sections of brain following internal carotid artery infusion of 5-nm colloidal gold conjugates of UPC10 (UPC10-Au). The morphologically observed binding of UPC10-Au to brain microvessels may be induced by gold conjugation. These studies describe the use of gold conjugates of antibodies to delineate the subcellular pathway involved in transcytosis through the BBB.

Brain delivery of biotin bound to a conjugate of neutral avidin and cationized human albumin

The delivery of pharmaceuticals through the brain capillary endothelial wall, which makes up the blood-brain barrier (BBB) in vivo, may be facilitated by conjugation of therapeutics to brain drug delivery vectors. Since cationized albumin has been shown to undergo absorptive-mediated transcytosis through the BBB in vivo, cationized human serum albumin (cHSA) is a potential brain drug delivery vector in humans. Conjugation of biotinylated therapeutics to brain drug delivery vectors is facilitated by the preparation of vector/avidin conjugates. Therefore, the present studies describe the preparation of a cHSA-avidin conjugate and the delivery of 3H-biotin bound to this conjugate through the BBB in vivo in anesthetized rats. Since the cationic nature of avidin (AV) accelerates the removal of avidin-based conjugates from blood in vivo, the present studies also describe the preparation and the pharmacokinetics of 3H-biotin bound to a conjugate of cHSA and neutral avidin (NLA). The bifunctional nature of the conjugate was retained: the cHSA/NLA conjugate contained 2.8 to 6.8 biotin binding sites per conjugate, and the BBB permeability-surface area (PS) product for 3H-biotin bound to cHSA/NLA was at least 7-fold greater than the BBB PS product for 3H-biotin bound to a conjugate of NLA and native HSA (nHSA). The systemic clearance of the cHSA conjugate was reduced 10-fold by the use of NLA as opposed to AV. The increased area under the plasma concentration curve (AUC) of the cHSA-NLA conjugate correlated with an increase in brain delivery of 3H-biotin as compared to the brain delivery achieved with the cHSA/AV conjugate.(ABSTRACT TRUNCATED AT 250 WORDS)

Treatment response with transurethral radiofrequency thermotherapy for symptomatic benign prostatic hyperplasia

One hundred and two patients with benign prostatic hyperplasia were treated by transurethral radio-frequency thermotherapy (TURT) device (Thermex-II, Direx, Israel) with 47.5 degrees C in single session for 2 hours and 30 minutes from November 1992 to October 1993. Among them, 83 patients, who were followed up for more than 3 months were included in this study. Twenty-seven (32.5%) patients had a history of acute retention. Pretreated values of the mean Madsen-Iversen symptom score, maximum urine flow rate, postvoiding residual urine volume, prostate volume and prostate specific antigen (PSA) were 15.4, 6.5 ml/sec, 61.3ml, 43.2ml and 0.77 ng/ml respectively. Madsen-Iversen symptom score, maximum urine flow rate were measured at 2 weeks, 1, 3 and 6 months after TURT. The residual urine volume, prostate volume and PSA level were measured at 3 and 6 months after TURT. During the follow up, the symptom score started to decrease significantly at 1 month (9.9, p < 0.01) after TURT, and gradually decreased up to 6.9 at 3 months. The maximum flow rate showed initial significant improvement at 2 weeks (8.1 ml/sec., p < 0.01), but no significant interval change was observed thereafter. The residual volume decreased significantly at 3 months (41.3 ml, p < 0.01) and no decrement was noted until 6 months. Neither the prostate volume nor PSA value changed significantly at 3 or 6 months after TURT. The improvement, which was defined as a change of 50% or more in at least one of subjective or objective symptoms showed in 63.9% (53/83) at 3 months and 57.1% (32/56) at 6 months. Both subjective and objective improvements at 3 and 6 months after treatment showed in 24.1% and 19.6%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Structural aspects of the reversal phase of alveolar bone remodelling

The ultrastructure of the reversal line during alveolar bone remodelling was investigated in the rat. Surface bone remodelling along the periosteum of the mandible was induced by the extraction of opposing maxillary molars. With transmission EM the reversal line was seen to be composed of a superficial electron-dense amorphous layer and a deep filamentous layer at 7 d after extraction. The reversal line exhibited strong alkaline phosphatase activity and contained acid mucopolysaccharide. Scanning EM of the surface of the line, exposed by sonication in distilled water, showed papillary structures, the surface of which appeared granular and exhibited a crystalline appearance. The tips of collagen fibrils of new bone were attached to the top of the papillae in the front area of bone formation. It is suggested that the reversal line is involved in the coupling of bone resorption and formation.

Transport of human recombinant brain-derived neurotrophic factor (BDNF) through the rat blood-brain barrier in vivo using vector-mediated peptide drug delivery

The blood-brain barrier (BBB) transport of brain-derived neurotrophic factor (BDNF) in anesthetized rats was examined in the present studies using vector-mediated peptide drug delivery. Following tritiation, the BDNF was biotinylated via a disulfide linker and was coupled to a covalent conjugate of neutral avidin (NLA), which binds the biotinylated peptide with a high affinity, and the murine OX26 monoclonal antibody to the rat transferrin receptor. Owing to the abundance of transferrin receptors on brain capillary endothelium, the OX26 monoclonal antibody undergoes receptor-mediated transcytosis through the BBB, and the NLA-OX26 conjugate transports biotinylated peptide therapeutics through the BBB. The present studies show that while unconjugated BDNF was not transported through the BBB in vivo, the conjugation of biotinylated BDNF to the NLA-OX26 vector resulted in a marked increase in the brain delivery of BDNF, as defined by measurements of the percentage of the injected dose (ID) delivered per gram of brain. Although BDNF was not transported through the BBB in vivo, this cationic peptide was avidly bound by isolated human brain capillaries via a low-affinity, high-capacity system that was inhibited by protamine and by serum protein binding of BDNF. In conclusion, these studies show that the delivery of unconjugated BDNF to brain is nil owing to the combined effects of negligible BBB transport and rapid systemic clearance of intravenous administered BDNF. The brain delivery of BDNF may be augmented by conjugation of BDNF to BBB drug delivery vectors, such as the NLA-OX26 conjugate.

Use of neutral avidin improves pharmacokinetics and brain delivery of biotin bound to an avidin-monoclonal antibody conjugate

The delivery of therapeutic agents through the brain capillary endothelial wall, which makes up the blood-brain barrier (BBB) in vivo, is enabled by coupling drugs to brain drug delivery transport vectors, such as the OX26 monoclonal antibody to the transferrin receptor located on the BBB. Drug conjugation to delivery vectors is possible by the use of avidin/biotin technology, and the production of avidin/vector conjugates potentially allows for the delivery through the BBB of many biotinylated therapeutics. However, the use of avidin causes reduced brain delivery of avidin/vector conjugates, because of the rapid systemic clearance of such conjugates from the bloodstream. Because previous studies have shown that this rapid elimination is due to avidin's cationic nature, the present studies describe the production of neutral avidin-OX26 antibody conjugates. Isoelectric focusing demonstrated the pls of avidin and neutral avidin were > 9 and 5 to 6, respectively. Neutral avidin and the OX26 antibody, which was purified from serum-free hybridoma-conditioned supernatants, were conjugated with a thio-ether linkage. The area under the plasma concentration curve of [3H] biotin/neutral avidin-OX26 was more than 5-fold greater than that for [3H] biotin/avidin-OX26. The mean residence time of [3H] biotin/neutral avidin-OX26 in plasma was 11.3 +/- 0.2 hr. The BBB permeability-surface area product was not significantly different for either [3H] biotin/neutral avidin-OX26 or [3H] biotin/avidin-OX26. The delivery of [3H] biotin to brain reached 0.20 to 0.25% of injected dose per gram brain by 2-6 hr after single intravenous injection, whereas the brain delivery of [3H] biotin/avidin-OX26 did not exceed 0.05% injected dose per g.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of beta-lactamase as a secreted reporter of promoter function in yeast

K1 preprotoxin is the 316 residue precursor of the K1 killer toxin secreted by the yeast Saccharomyces cerevisiae. The SP beta la reporter consists of the mature, secreted form of beta-lactamase (beta la) fused to S and P, two fragments of preprotoxin. S is the N-terminal 34 residues, including the secretion signal. P, a 67 residue 'processing' segment with three sites for N-glycosylation, terminates in a Lys Arg site for cleavage by the Kex2 protease. Expression of SP beta 1a in yeast results in efficient secretion, processing by signal peptidase and glycosylation in the endoplasmic reticulum, producing pro beta la. Kex2 cleavage of pro beta la in the lumen of a late Golgi compartment releases beta la, which accumulates stably in culture media buffered at pH 5.8-7. The half-life of secretion is 11 min at 30 degrees C; 10-12% of the total activity in exponential-phase cells is intracellular, mostly in the form of pro beta la, indicating that transit from the endoplasmic reticulum to the Golgi is rate limiting. We have used SP beta la expression in single- and multi-copy vectors to compare the PGK, GAL1, GAL10, PHO5 and CUP1 promoters under varying nutritional conditions. In exponential-phase cells, secretion of beta la over a 40-fold range and up to several micrograms/ml was proportional to transcript level, demonstrating that SP beta la can be employed as a convenient secreted reporter of promoter function in yeast.

Blood-brain barrier transport and brain metabolism of adenosine and adenosine analogs

Adenosine transport through the brain capillary endothelial wall, which makes up the blood-brain barrier (BBB) in vivo, is mediated by a saturable transport system that has not been characterized extensively. Moreover, the inability of adenosine to augment cerebral blood flow in most species after intracarotid adenosine administration suggests the presence of an enzymatic BBB to circulating adenosine. Therefore, the present studies investigate the Michaelis-Menten kinetics of BBB adenosine transport and the rate of cerebral metabolism of circulating adenosine after internal carotid artery perfusion in anesthetized rats. The studies also assess the ability of various adenosine analogues to inhibit [3H]adenosine transport at the BBB in vivo. Initial rates of BBB transport of adenosine in vivo were observed for at least 15 sec of internal carotid artery perfusion. BBB adenosine transport was partially sodium-dependent and was saturable with the following kinetic parameters: Km = 1.1 +/- 0.2 microM; Vmax = 202 +/- 44 pmol/min/g; and KD = 34 +/- 6 microliters/min/g. BBB transport of [3H]adenosine was not inhibited by cyclohexyladenosine or S-(4-nitrobenzyl)-6-thioinosine, but was inhibited by dipyridamole (Ki = 2.2 +/- 0.9 microM). Capillary depletion studies were performed, which demonstrated sequestration of [3H] radioactivity by the microvascular pellet after carotid arterial infusion of [3H]adenosine. Only 10 +/- 3% of cerebral [3H] radioactivity resided in the free adenosine pool after 15 sec of internal carotid artery perfusion of [3H]adenosine and rapid termination of brain metabolism with microwave irradiation.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics and saturable blood-brain barrier transport of biotin bound to a conjugate of avidin and a monoclonal antibody to the transferrin receptor

The delivery of biotinylated therapeutics through the blood-brain barrier (BBB) may be facilitated by the use of avidin-based chimeric peptide conjugates. The latter are formed by conjugating avidin to a BBB drug delivery vector, which is a protein that undergoes receptor-mediated transcytosis through the BBB. The murine OX26 monoclonal antibody to the rat transferrin receptor undergoes receptor-mediated transport through the BBB, and previous studies have shown that a [3H]biotin/avidin-OX26 conjugate is effectively transported through the BBB. However, avidin is a cationic protein, which causes a marked increase in the systemic clearance of avidin-based conjugates from the plasma compartment. The present studies describe attempts to elevate the reduced plasma area under the curve (AUC) of [3H]biotin/avidin-OX26 by preloading or coloading with unconjugated OX26 antibody or unconjugated avidin. Both systemic clearance and BBB transport of avidin-OX26 were equally affected by OX26 preloading or coloading; this had inverse effects on the plasma AUC and the BBB permeability surface area product with no resulting change in the fractional delivery of [3H]biotin to brain. Conversely, avidin coloading preferentially reduced brain clearance of the [3H]biotin/avidin-OX26 conjugate, without substantial alteration in the plasma AUC and greatly reduced the fractional delivery of [3H]biotin to brain. In summary, these studies show that the use of avidin-based vectors results in rapid systemic clearance, which causes a reduction in the delivery of [3H]biotin to brain, despite a comparable BBB permeability coefficient for either the unconjugated OX26 antibody or the avidin-OX26 conjugate.

Protamine-mediated transport of albumin into brain and other organs of the rat. Binding and endocytosis of protamine-albumin complex by microvascular endothelium

High doses of intravenous protamine cause generalized vascular permeability changes in brain and other organs, and concomitant hypoproteinemia. The present investigations test the hypothesis that protamine has a dual action of both binding serum proteins and of undergoing absorptive-mediated transcytosis through microvascular endothelial barriers. Binding of albumin to protamine was demonstrated using equilibrium dialysis, and protamine was shown to selectively augment the uptake of albumin, but not sucrose, in isolated bovine or human brain capillaries. In contrast, the anionic macromolecule, dextran sulfate, resulted in an increased capillary uptake of both albumin and sucrose in vitro. The selective effects of protamine on albumin transport were also documented in vivo using an external organ technique; the intravenous injection of 1.5 mg/kg protamine resulted in a marked and selective influx of albumin into brain, heart, kidney, lung, and liver, and the increased albumin transport exceeded the increased sucrose uptake in some organs by an order of magnitude. The transcytosis of protamine through the cerebral microvascular barrier was documented with an internal carotid artery perfusion technique. In summary, these studies provide evidence for protamine-mediated vectorial transport of albumin through microvascular barriers in brain and other organs.

Localization of abnormal parathyroid glands of the mediastinum with MR imaging

PURPOSE

To determine the sensitivity of magnetic resonance (MR) imaging for preoperative localization of abnormal parathyroid glands in the mediastinum and to compare the sensitivity of MR imaging with those of scintigraphy and ultrasonography (US).

MATERIALS AND METHODS

The prospective sensitivity of MR imaging was compared with those of thallium-technetium scintigraphy and US in 25 patients in whom the abnormal gland was located in the mediastinum at surgery.

RESULTS

MR imaging had a much higher sensitivity (22 of 25 cases [88%]) than did scintigraphy (11 of 19 cases [58%]) or US (three of 24 cases [12%]). The most common locations for the mediastinal gland were intrathymic (eight of 25 cases) and paraesophageal (six of 25 cases) sites.

CONCLUSION

MR imaging should be considered the modality of choice for preoperative localization in this group of patients.

Bacterial biofilm formation on the bladder epithelium of spinal cord injured patients. II. Toxic outcome on cell viability

As a follow up to our first study of 10 spinal cord injured patients, a further 8 patients were investigated over 2 months for biofilm formation on their bladder epithelial cells and for evidence that these uropathogens damage the host bladder. All the patients were found to be colonized with uropathogens, regardless of whether or not they were receiving antibiotics. Using vital staining, it was discovered that there was a significant reduction (33%) in bladder cell viability in the presence of bacterial biofilms compared to controls. This was not associated with cell turnover rates. In vitro tests showed a similar reduction in cell viability when uropathogens were incubated with bladder cells. In addition, white cell counts were significantly elevated in the patients' urine, indicative of an infectious and/or inflamed state. There was no difference between symptomatic and asymptomatic patients in their mean bacterial adhesion counts. Patients were just as likely to be symptomatic as asymptomatic when on antibiotics. In summary, the presence of virulent organisms in the bladder does adversely affect the host, even when the patient has insignificant signs and symptoms of infection, thereby raising concerns over the decision not to treat the patient. Unless specific antibiotics are used which eradicate adherent biofilms from the bladder, the treatment of symptomatic patients will only impact upon the signs and symptoms in some patients, and not alter their susceptibility to reinfection.

Microbial adhesion and biofilm formation on ureteral stents in vitro and in vivo

Thirty ureteral stents, inserted for 5 to 128 days following extracorporeal shock wave lithotripsy, were examined for the presence of bacterial biofilms. Of these, 90% had adherent pathogens (44% mixed organisms) on the stents, 45% of which were present in low numbers (10(1)-10(2) per 1 cm3 section) and 55% were in small and large microcolony biofilms (> 2 x 10(2)-10(7)). The organisms were recovered from the stents even though urine culture was only positive in 27% of patients. Of the organisms isolated, 77% were Gram positive cocci, 15% Gram negative rods and 8% Candida. No blockage of the stents occurred. All of the patients had received antimicrobial therapy post-insertion, and in 15 cases biofilms were found while on treatment. None of the patients received therapy for urinary tract infections while the stent remained in place. In vitro experiments demonstrated the ability of Escherichia coli, Proteus mirabilis, Staphylococcus epidermidis and Enterococcus faecalis uropathogens to adhere and form biofilms on ureteral stents within 24 hours. Clearly, bacterial biofilms do occur on ureteral stents and urinary culture may not detect their presence. The high recovery rate of Gram positive organisms may indicate a preferential adhesion to the biomaterial surface. The findings also indicate that unlike biofilm formation on many other prosthetic implants, colonization with Gram positive organisms on ureteral stents does not necessarily coincide with the development symptomatic infection.

Bacterial biofilm formation in the urinary bladder of spinal cord injured patients

Ten spinal cord injured patients aged 8 to 55 years (mean 32) were followed for up to 2 months after admission to a rehabilitation setting from an acute care hospital. Urinary fluid and bladder epithelial cells were collected weekly by intermittent catheterization and examined for bacterial colonization. Six patients had no history of urinary tract infection upon admission, likely due to the antimicrobial coverage given during acute care. All the patients subsequently became colonized with uropathogens at some time during the study period. Bacterial biofilms were found in 73% of the samples (73% Gram negative organisms, 27% Gram positive), with mean pathogenic adhesion counts of 29 organisms per bladder cell. In 16% of cases, bladder biofilms were found when urine culture was negative. Bacterial biofilms were also evident during antimicrobial therapy in 10 of 12 samples tested and urine cultures showed breakthrough infections in 50% of cases. Two asymptomatic patients were colonized with Klebsiella pneumoniae and Pseudomonas aeruginosa and were dismissed without requiring therapy. Clearly, bacterial biofilms can exist on bladder epithelia, without being detected in urine samples and without giving rise to symptoms. The extent to which they occur and damage the host remains to be determined, as does the answer to the question, should these patients be treated?

Evaluation of marrow perfusion in the femoral head by dynamic magnetic resonance imaging. Effect of venous occlusion in a dog model

RATIONALE AND OBJECTIVES

There is a continuing need for a greater sensitivity of magnetic resonance imaging (MRI) in the diagnosis of avascular necrosis (AVN). Previously, it was demonstrated that a dynamic MRI method, with gadolinium-DTPA (Gd-DTPA) enhancement, can detect acute changes not seen on spin-echo images after arterial occlusion in a dog model. Because venous congestion appears to be a more directly relevant hemodynamic abnormality in a majority of clinical AVN cases, the authors extended the dynamic MRI technique to study changes in venous occlusion.

METHODS

Dynamic MRI of the proximal femur was performed in five adult dogs before and after unilateral ligation of common iliac and lateral circumflex veins. Sixteen sequential gradient-recalled pulse sequence (GRASS) images (time resolution = 45 mseconds, echo time = 9 mseconds, flip angle = 65 degrees) were obtained immediately after a bolus intravenous injection of 0.2 mmol/kg of Gd-DTPA. Simultaneous measurements of regional blood flow were made using the radioactive microsphere method.

RESULTS

After venous ligation, there was a 25% to 45% decrease in the degree of enhancement compared with preligation values on the ligated side. The decrease in cumulative enhancement (integrated over the entire time course) was statistically significant. The occlusion technique was verified by confirming a statistically significant decrease in blood flow determined by the microsphere method.

CONCLUSIONS

Dynamic Gd-DTPA-enhanced fast MRI technique can detect acute changes in bone marrow perfusion due to venous occlusion. This technique may have applications in the early detection of nontraumatic AVN.

Nonfunctional paraganglioma of the liver

Paragangliomas occurring in the liver are rare. We report a patient with a history of nonfunctional paragangliomas in the head and neck who developed liver metastases years later. We discuss findings on cross-sectional imaging modalities, including magnetic resonance imaging (MRI), which demonstrate the hypervascular nature of the liver masses.

Bone marrow perfusion evaluated with gadolinium-enhanced dynamic fast MR imaging in a dog model

The authors studied, in a dog model, the feasibility of using gadolinium-enhanced dynamic magnetic resonance (MR) imaging to noninvasively monitor bone marrow perfusion of the proximal femur. With a gradient-recalled acquisition, sequential images of 10 hips in five healthy dogs were obtained for 14 minutes after an intravenous bolus injection of 0.2 mmol of gadopentetate dimeglumine per kilogram. The study was repeated after unilateral arterial embolization of major femoral vessels. Radiolabeled microspheres were injected before and after vessel occlusion. After unilateral embolization, statistically significant differences in enhancement were observed between embolized and control sides (eg, 31% vs 83% average peak enhancement in the femoral neck). There was a high correlation (r = .81 [average]) between the MR data and the microsphere blood flow measurements. The postembolization data indicate that contrast-enhanced fast MR imaging may allow early detection of abnormal bone marrow flow. This technique may be valuable in evaluating patients at risk for avascular necrosis of the femoral head, especially in posttraumatic cases.