Biomedical subjects

T P Davis

Publications and source records attributed to T P Davis.

At least 19 recordsLinked to original sources

PubMed2005

Alterations in blood-brain barrier ICAM-1 expression and brain microglial activation after lambda-carrageenan-induced inflammatory pain.

Previous studies showed that peripheral inflammatory pain increased blood-brain barrier (BBB) permeability and altered tight junction protein expression and the delivery of opioid analgesics to the brain. What remains unknown is which pathways and mediators during peripheral inflammation affect BBB function and structure. The current study investigated effects of lambda-carrageenan-induced inflammatory pain (CIP) on BBB expression of ICAM-1. We also examined the systemic contribution of a number of proinflammatory cytokines and microglial activation in the brain to elucidate pathways involved in BBB disruption during CIP. We investigated ICAM-1 RNA and protein expression levels in isolated rat brain microvessels after CIP using RT-PCR and Western blot analyses, screened inflammatory cytokines during the time course of inflammation, assessed white blood cell counts, and probed for BBB and central nervous system stimulation and leukocyte transmigration using immunohistochemistry and flow cytometry. Results showed an early increase in ICAM-1 RNA and protein expression after CIP with no change in circulating levels of several proinflammatory cytokines. Changes in ICAM-1 protein expression were noted at 48 h. Immunohistochemistry showed that the induction of ICAM-1 was region specific with increased expression noted in the thalamus and frontal and parietal cortices, which directly correlated with increased expression of activated microglia. The findings of the present study were that CIP induces increased ICAM-1 mRNA and protein expression at the BBB and that systemic proinflammatory mediators play no apparent role in the early response (1-6 h); however, brain region-specific increases in microglial activation suggest a potential for a central-mediated response.

Animals↗

PubMed2004

Survival of the d-wave superconducting state near the edge of antiferromagnetism in the cuprate phase diagram.

In the cuprate superconductor YBa2Cu3O6+x, hole doping in the CuO2 layers is controlled by both oxygen content and the degree of oxygen ordering. At the composition YBa2Cu3O6.35, the ordering can occur at room temperature, thereby tuning the hole doping so that the superconducting critical temperature gradually rises from 0 to 20 K. Here we exploit this to study the c-axis penetration depth as a function of temperature and doping. The temperature dependence shows the d-wave superconductor surviving to very low doping, with no sign of another ordered phase interfering with the nodal quasiparticles. The only apparent doping dependence is a smooth decline of superfluid density as T(c) decreases.

Journal Article↗

PubMed2002

Blood-brain barrier tight junctions are altered during a 72-h exposure to lambda-carrageenan-induced inflammatory pain.

In this study, we examined the effect of lambda-carrageenan-induced inflammatory pain on the functional and structural properties of the rat blood-brain barrier (BBB) over a 72-h time period. Systemic inflammation was induced by an intraplantar injection of 3% lambda-carrageenan into the right hind paw of female Sprague-Dawley rats. In situ brain perfusion and Western blot analyses were performed at 1, 3, 6, 12, 24, 48, and 72 h. In situ brain perfusion showed lambda-carrageenan significantly increased brain uptake of [(14)C]sucrose at 1, 3, 6, and 48 h (139 +/- 9%, 166 +/- 19%, 138 +/- 13%, and 146 +/- 7% compared with control, respectively). Capillary depletion analysis insured the increased brain uptake was due to increased BBB permeability and not vascular trapping. Western blot analyses for zonula occludens-1 (ZO-1) and occludin were performed on isolated cerebral microvessels. ZO-1 expression was significantly increased at 1, 3, and 6 h and returned to control expression levels by 12 h. Total occludin expression was significantly reduced at 1, 3, 6, 12, and 48 h. This investigation demonstrated that lambda-carrageenan-induced inflammatory pain elicits a biphasic increase in BBB permeability with the first phase occurring from 1-6 h and the second phase occuring at 48 h. Furthermore, changes in BBB function are correlated with altered tight junctional protein expression of occludin and ZO-1. Changes in the structure of tight junctions may have important clinical ramifications concerning central nervous system homeostasis and therapeutic drug delivery.

Animals↗

PubMed2001

Effect of reduced flow on blood-brain barrier transport systems.

Pathological states (i.e. stroke, cardiac arrest) can lead to reduced blood flow to the brain potentially altering blood-brain barrier (BBB) permeability and regulatory transport functions. BBB disruption leads to increased cerebrovascular permeability, an important factor in the development of ischemic brain injury and edema formation. In this study, reduced flow was investigated to determine the effects on cerebral blood flow (CBF), pressure, basal BBB permeability, and transport of insulin and K+ across the BBB. Anesthetized adult female Sprague-Dawley rats were measured at normal flow (3.1 ml min(-1)), half flow (1.5 ml min(-1)), and quarter flow (0.75 ml min(-1)), using bilateral in situ brain perfusion for 20 min followed by capillary depletion analysis. Reduction in perfusion flow rates demonstrated a modest reduction in CBF (1.27-1.56 ml min(-1) g(-1)), a decrease in pressure, and no significant effect on basal BBB permeability indicating that autoregulation remained functional. In contrast, there was a concomittant decrease in BBB transport of both insulin and K+ with reduced flow. At half and quarter flow, insulin transport was significantly reduced (R(Br)%=17.2 and R(Br)%=16.2, respectively) from control (R(Br)%=30.4). Additionally, a significant reduction in [86Rb+] was observed at quarter flow (R(Br)%=2.5) as compared to control (R(Br)%=4.8) suggesting an alteration in ion homeostasis as a result of low flow. This investigation suggests that although autoregulation maintains CBF, BBB transport mechanisms were significantly compromised in states of reduced flow. These flow alterations may have a significant impact on brain homeostasis in pathological states.

Animals↗

PubMed2001

Molecular physiology and pathophysiology of tight junctions in the blood-brain barrier.

Disruption of the tight junctions (TJs) of the blood-brain barrier (BBB) is a hallmark of many CNS pathologies, including stroke, HIV encephalitis, Alzheimer's disease, multiple sclerosis and bacterial meningitis. Furthermore, systemic-derived inflammation has recently been shown to cause BBB tight junctional disruption and increased paracellular permeability. The BBB is capable of rapid modulation in response to physiological stimuli at the cytoskeletal level, which enables it to protect the brain parenchyma and maintain a homeostatic environment. By allowing the "loosening" of TJs and an increase in paracellular permeability, the BBB is able to "bend without breaking"; thereby, maintaining structural integrity.

Animals↗

PubMed2001

SR48692 is a neurotensin receptor antagonist which inhibits the growth of small cell lung cancer cells.

Neurotensin (NT) is an autocrine growth factor for some small cell lung cancer (SCLC) cells. In this communication, the effects of a non-peptide NT receptor antagonist, SR48692, were investigated using SCLC cells. (3)H-SR48692 bound with high affinity (IC(50) = 20 nM) to NCI-H209 cells. Also, NT and SR48692 inhibited specific (125)I-NT binding with high affinity (IC(50) values of 2 and 200 nM). In contrast, the NT(2) receptor agonist, levocabastine, had little effect on specific (125)I-NT binding, second messenger production and proliferation using NCI-H209 cells. SR48692 (5 microM) antagonized the ability of NT (10 nM) to cause elevated cytosolic Ca2+ in Fura-2 AM loaded NCI-H209 cells. SR48692 antagonized the ability of NT to cause elevation of c-fos mRNA in these cells. Using a MTT proliferation assay, SR48692 inhibited NCI-H209 and H345 proliferation in a concentration-dependent manner. Using a clonogenic assay, 1 microM SR48692, reduced NCI-H209 colony number. Also, SR48692 (0.4 mg/kg per day) inhibited NCI-H209 xenograft proliferation in nude mice. These results suggest that SR48692 is a NT(1) receptor antagonist which inhibits SCLC growth.

Animals↗

PubMed2001

Peptide drug modifications to enhance bioavailability and blood-brain barrier permeability.

Peptides have the potential to be potent pharmaceutical agents for the treatment of many central nervous system derived maladies. Unfortunately peptides are generally water-soluble compounds that will not enter the central nervous system, via passive diffusion, due to the existence of the blood-brain barrier. Peptides can also undergo metabolic deactivation by peptidases, thus further reducing their therapeutic benefits. In targeting peptides to the central nervous system consideration must be focused both on increasing bioavailability and enhancing brain uptake. To date multiple strategies have been examined with this focus. However, each strategy comes with its own complications and considerations. In this review we assess the strengths and weaknesses of many of the methods currently being examined to enhance peptide entry into the central nervous system.

Biological Availability↗

PubMed2001

Inflammatory pain alters blood-brain barrier permeability and tight junctional protein expression.

Effects of inflammatory pain states on functional and molecular properties of the rat blood-brain barrier (BBB) were investigated. Inflammation was produced by subcutaneous injection of formalin, lambda-carrageenan, or complete Freund's adjuvant (CFA) into the right hind paw. In situ perfusion and Western blot analyses were performed to assess BBB integrity after inflammatory insult. In situ brain perfusion determined that peripheral inflammation significantly increased the uptake of sucrose into the cerebral hemispheres. Capillary depletion and cerebral blood flow analyses indicated the perturbations were due to increased paracellular permeability rather than vascular volume changes. Western blot analyses showed altered tight junctional protein expression during peripheral inflammation. Occludin significantly decreased in the lambda-carrageenan- and CFA-treated groups. Zonula occluden-1 expression was significantly increased in all pain models. Claudin-1 protein expression was present at the BBB and remained unchanged during inflammation. Actin expression was significantly increased in the lambda-carrageenan- and CFA-treated groups. We have shown that inflammatory-mediated pain alters both the functional and molecular properties of the BBB. Inflammatory-induced changes may significantly alter delivery of therapeutic agents to the brain, thus affecting dosing regimens during chronic pain.

Actins↗

PubMed2001

Results with abdominal vascular trauma in the modern era.

This is a report of a 10-year experience (1989-1998) with 300 consecutive patients found to have an injury to a named abdominal vessel at the time of an exploratory laparotomy for trauma. An abdominal gunshot wound was the mechanism of injury in 78 per cent of patients, and injury to more than one named abdominal vessel was present in 42 per cent. The abdominal aorta, inferior vena cava, and external iliac artery and vein were the most commonly injured vessels. When management for the five most commonly injured arteries was grouped, exsanguination before attempts at repair occurred in 11 to 15 per cent of patients and the mean survival in the remainder was 46 per cent. When management for the five most commonly injured veins was grouped, exsanguination before attempts at repair occurred in 5 per cent of patients and the mean survival in the remainder was 64 per cent. A number of administrative and medical changes in the management of patients with abdominal trauma occurred from 1992 through 1994. Despite significantly increased Injury Severity Scores for patients treated from 1993 through 1998 as compared with those treated from 1989 through 1992 survival rates for patients with injuries to the abdominal aorta and inferior vena cava were unchanged. Survival rates for injuries to the external iliac artery and vein increased significantly. The local changes in management should be considered for prospective studies in other urban trauma centers.

Adolescent↗

PubMed2001

Pharmacodynamic and pharmacokinetic characterization of poly(ethylene glycol) conjugation to met-enkephalin analog [D-Pen2, D-Pen5]-enkephalin (DPDPE).

Poly(ethylene glycol), or PEG, conjugation to proteins and peptides is a growing technology used to enhance efficacy of therapeutics. This investigation assesses pharmacodynamic and pharmacokinetic characteristics of PEG-conjugated [D-Pen2,D-Pen5]-enkephalin (DPDPE), a met-enkephalin analog, in rodent (in vivo, in situ) and bovine (in vitro) systems. PEG-DPDPE showed increased analgesia (i.v.) compared with nonconjugated form (p < 0.01), despite a 172-fold lower binding affinity for the delta-opioid receptor. [125I]PEG-DPDPE had a 36-fold greater hydrophilicity (p < 0.01) and 12% increase in the unbound plasma protein fraction (p < 0.01), compared with [(125)I]DPDPE. [125I]PEG-DPDPE had a 2.5-fold increase in elimination half-life (p < 0.01), 2.7-fold decrease in volume of distribution (p < 0.01), and a 7-fold decrease in plasma clearance rate (p < 0.01) to [125I]DPDPE. Time course distribution showed significant concentration differences (p < 0.01) in plasma, whole blood, liver, gallbladder, gastrointestinal (GI) content, GI tract, kidneys, spleen, urine, and brain (brain, p < 0.05), between the conjugated and nonconjugated forms. Increased brain uptake of [(125)I]PEG-DPDPE corresponded to analgesia data. [125I]PEG-DPDPE in brain was shown to be 58.9% intact, with 41.1% existing as [125I]DPDPE (metabolite), whereas [125I]DPDPE was 25.7% intact in the brain (at 30 min). In vitro P-glycoprotein affinity was shown for [125I]DPDPE (p < 0.01) but not shown for [125I]PEG-DPDPE. In vitro saturable uptake, with 100 microM DPDPE, was shown for [125I]PEG-DPDPE (p < 0.05). In this study, PEG-conjugated DPDPE seems to act as a prodrug, enhancing peripheral pharmacokinetics, while undergoing hydrolysis in the brain and allowing nonconjugated DPDPE to act at the receptor.

Analgesics, Opioid↗

PubMed2001

Improved blood-brain barrier penetration and enhanced analgesia of an opioid peptide by glycosylation.

Neuropeptide pharmaceuticals have potential for the treatment of neurological disorders, but the blood-brain barrier (BBB) limits entry of peptides to the brain. Several strategies to improve brain delivery are currently under investigation, including glycosylation. In this study we investigated the effect of O-linked glycosylation on Ser(6) of a linear opioid peptide amide Tyr-D-Thr-Gly-Phe-Leu-Ser-NH(2) on metabolic stability, BBB transport, and analgesia. Peptide stability was studied in brain and serum from both rat and mouse by high-performance liquid chromatography. BBB transport properties were investigated by rat in situ perfusion. Tail-flick analgesia studies were performed on male ICR mice, injected i.v. with 100 microg of peptide ligand. Glycosylation of Ser(6) of the peptide led to a significant increase in enzymatic stability in both serum and brain. Glycosylation significantly increased the BBB permeability of the peptide from a value of 1.0 +/- 0.2 microl x min(-1) x g(-1) to 2.2 +/- 0.2 microl x min(-1) x g(-1) (p < 0.05), without significantly altering the initial volume of distribution. Analgesia studies showed that the glycosylated peptide gave a significantly improved analgesia after i.v. administration compared with nonglycosylated peptide. The improved analgesia profile shown by the glycosylated peptide is due in part to an improvement in bioavailability to the central nervous system. The bioavailability is increased by improving stability and transport into the brain.

Analgesics, Opioid↗

PubMed2000

Improved bioavailability to the brain of glycosylated Met-enkephalin analogs.

The blood-brain barrier prevents the entry of many potentially therapeutic peptide drugs to the brain. Glycosylation has shown potential as a methodology for improving delivery to the CNS. Previous studies have shown improved bioavailability and improved centrally mediated analgesia of glycosylated opioids. In this study we investigate the effect of glycosylation on the cyclic opioid peptide [D-Cys(2,5),Ser(6),Gly(7)] enkephalin. The peptide was glycosylated on the Ser(6) via an O-linkage with various sugar moieties and alignments. The peptides were then investigated for receptor binding, physiochemical attributes, in situ brain uptake in female Sprague-Dawley rats and antinociception in male ICR mice. Glycosylation resulted in a slight decrease in affinity to the delta-opioid receptor, and mixed effect on binding to the mu-opioid receptor. There was a significant decrease in lipophilicity resulting from glycosylation and a slight reduction in binding to bovine serum albumin. In situ perfusion showed that brain uptake was improved by up to 98% for several of the glycosylated peptides, and the nociceptive profiles of the peptides, in general, followed the rank order of peptide entry to the brain with up to a 39-fold increase in A.U.C.

Animals↗

PubMed2000

Enkephalin glycopeptide analogues produce analgesia with reduced dependence liability.

Endogenous peptides (e.g. enkephalins) control many aspects of brain function, cognition, and perception. The use of these neuroactive peptides in diverse studies has led to an increased understanding of brain function. Unfortunately, the use of brain-derived peptides as pharmaceutical agents to alter brain chemistry in vivo has lagged because peptides do not readily penetrate the blood-brain barrier. Attachment of simple sugars to enkephalins increases their penetration of the blood-brain barrier and allows the resulting glycopeptide analogues to function effectively as drugs. The delta-selective glycosylated Leu-enkephalin amide 2, H(2)N-Tyr-D-Thr-Gly-Phe-Leu-Ser(beta-D-Glc)-CONH(2), produces analgesic effects similar to morphine, even when administered peripherally, yet possesses reduced dependence liability as indicated by naloxone-precipitated withdrawal studies. Similar glycopeptide-based pharmaceuticals hold forth the promise of pain relief with improved side-effect profiles over currently available opioid analgesics.

Analgesics, Opioid↗

PubMed2000

Bioavailability of Ziconotide in brain: influx from blood, stability, and diffusion.

Ziconotide is a selective peptide antagonist of the N-type calcium channel currently in clinical trials for analgesia. Ziconotide reached a maximal brain concentration of between 0.003 and 0.006% of the injected material per gram of tissue at 3-20 min after i.v. injection, and this decayed to below 0.001%/g after 2 h. The structurally distinct conopeptide SNX-185 (synthetic TVIA) was considerably more persistent in brain after i.v. administration, with 0.0035% of the injected material present at 2-4 h after i.v. injection, and 0.0015% present at 24 h. Similar results (i.e. greater persistence of SNX-185) were obtained when the peptides were perfused through in vivo dialysis probes implanted into the hippocampus. Image analysis and serial sectioning showed that diffusion of Ziconotide in the extracellular fluid around the dialysis probe was minimal, with the peptide located within 1 mm of the probe after 2 h. In vitro diffusion through cultured bovine brain microvessel endothelial cells (BBMEC) verified that a close structural analog of Ziconotide (SNX-194) passed through this blood-brain barrier (BBB) model as expected for peptides of similar physical properties (permeability coefficient of 6.5 x 10(-4) cm/g). Passage from blood to brain was also verified by in situ perfusion through the carotid artery. A statistically greater amount of radioactivity was found to cross the BBB after perfusion of radioiodinated Ziconotide compared to [14C]inulin. Capillary depletion experiments and HPLC analysis defined the brain location and stability.

Amino Acid Sequence↗

PubMed2000

Stroke: development, prevention and treatment with peptidase inhibitors.

Stroke is the leading cause of long-term disability in the United States and affects more people than any other neurologic disorder. Hypertension is a major risk factor associated with stroke. Several anti-hypertensive agents have been used to treat chronic hypertension to reduce the morbidity and mortality of stroke. Previous experimental studies have shown reduced stroke mortality with angiotensin-converting enzyme (ACE) inhibitors. This review discusses the development of stroke and potential use of ACE inhibitors in prevention and treatment of this disease. Furthermore, this review focuses on current investigations aimed at cellular mechanisms involved in stroke-induced microvascular alterations.

Antihypertensive Agents↗

PubMed2000

Assessment of stereoselectivity of trimethylphenylalanine analogues of delta-opioid [D-Pen(2),D-Pen(5)]-enkephalin.

[D-Pen(2),D-Pen(5)]-Enkephalin (DPDPE) is an enzymatically stable delta-opioid receptor-selective peptide, which was modified by the trimethylation of the Phe(4) residue to give beta-methyl-2', 6'-dimethylphenylalanine (TMP), resulting in four conformations : (2R,3S)-beta-Phe-DPDPE, (2R,3R)-beta-Phe-DPDPE, (2R, 3S)-beta-Phe-DPDPE, and (2S,3R)-beta-Phe-DPDPE. Synthesis was by solid-phase techniques using enantiomerically pure amino acids to give the four optically pure diastereoisomer peptides. The potency and selectivity (delta- versus mu-opioid receptor) were evaluated by radioreceptor binding in rat brain, with a mu/delta ratio decrease for all TMP conformations, compared with the parent compound (DPDPE). Octanol/buffer distribution analysis showed enhanced lipophilicity of all TMP forms, with a sixfold enhancement associated with (2S,3S)-TMP. In situ vascular perfusion in anesthetized rats showed a 1.6-fold (p < 0.01) increase in the ratio of brain uptake for (2S,3S)-TMP and a 1.5-fold (p < 0.01) decrease in uptake for (2R,3R)-TMP. Saturability of (2S,3S)-TMP was shown (p < 0.01) against 100 microM unlabeled DPDPE, showing a shared nondiffusionary transport system. P-glycoprotein affinity was shown in situ for the parent and (2S,3S)-TMP (p < 0.01). Protein binding capacity of the TMP compounds in rat plasma and in situ mammalian bovine serum albumin-Ringer showed (2R,3S)-TMP and (2S,3R)-TMP with the lowest degree of protein binding (p < 0.01), and (2S,3S)-TMP and (2R,3R)-TMP with comparable affinities to DPDPE. Analgesia, via intravenous administration, showed significantly reduced (p < 0.01) end effect and time course for (2R,3R)-TMP, (2R,3S)-TMP, and (2S, 3R)-TMP as compared with DPDPE. These results demonstrate that topographical modification in a conformationally restricted peptide can significantly modulate potency and receptor selectivity, binding capacity, enzymatic stability, lipophilicity, P-glycoprotein affinity, and blood-brain barrier permeability, resulting in a change of bioavailability, and thereby provides insight for future peptide drug design.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2000

Prohormone convertase and autocrine growth factor mRNAs are coexpressed in small cell lung carcinoma.

A hallmark of small cell lung carcinoma (SCLC) is the expression of autocrine growth factors such as neurotensin and gastrin-releasing peptide, which bind to cellular receptors and stimulate cell division. The biological activity of autocrine growth factors requires the concurrent expression of prohormone convertases that cleave the growth factors to their active form, suggesting the expression of these genes is linked in SCLCs. RNase protection assays were used to detect the expression of autocrine growth factor and prohormone convertase mRNAs in a panel of lung cancer cell lines. These mRNAs are coexpressed in SCLC and lung carcinoid cell lines, but not in normal lung epithelium or in non-small cell lung cancers. These findings, together with earlier results from our laboratory, suggest the expression of prohormone convertases has an important role in the development and maintenance of the SCLC phenotype and that autocrine growth factor and prohormone convertase genes respond to a common transcriptional activator in SCLC.

Carcinoma, Small Cell↗

PubMed2000

Doxycycline-induced esophageal ulceration in the U.S. Military service.

U.S. military forces are frequently deployed with little warning to regions of the world where chloroquine-resistant malaria is endemic. Doxycycline is often used for malaria chemoprophylaxis in these environments. The use of doxycycline can be complicated by esophageal injury. Two cases of esophageal ulceration will be discussed, followed by a review of the literature. Doxycycline causes esophageal injury through a combination of drug-specific factors, the circumstances of drug administration, and individual patient conditions. Patients with dysphagia attributable to esophageal ulceration are managed by intravenous fluid support and control of gastric acid reflux until their symptoms resolve over 5 to 7 days. The risk of esophageal injury can be minimized by use of fresh capsules, drug administration in the upright position well before lying down to sleep, and drinking at least 100 ml of water after swallowing the medication.

Adult↗