Blood soluble drag-reducing polymers prevent lethality from hemorrhagic shock in acute animal experiments

Over the past several decades, blood-soluble drag reducing polymers (DRPs) have been shown to significantly enhance hemodynamics in various animal models when added to blood at nanomolar concentrations. In the present study, the effects of the DRPs on blood circulation were tested in anesthetized rats exposed to acute hemorrhagic shock. The animals were acutely resuscitated either with a 2.5% dextran solution (Control) or using the same solution containing 0.0005% or 5 parts per million (ppm) concentration of one of two blood soluble DRPs: high molecular weight (MW=3500 kDa) polyethylene glycol (PEG-3500) or a DRP extracted from Aloe vera (AVP). An additional group of animals was resuscitated with 0.0075% (75 ppm) polyethylene glycol of molecular weight of 200 kDa (PEG-200), which possesses no drag-reducing ability. All of the animals were observed for two hours following the initiation of fluid resuscitation or until they expired. We found that infusion of the DRP solutions significantly improved tissue perfusion, tissue oxygenation, and two-hour survival rate, the latter from 19% (Control) and 14% (PEG-200) to 100% (AVP) and 100% (PEG-3500). Furthermore, the Control and PEG-200 animals that survived required three times more fluid to maintain their blood pressure than the AVP and PEG-3500 animals. Several hypotheses regarding the mechanisms underlying these observed beneficial hemodynamic effects of DRPs are discussed. Our findings suggest that the drag-reducing polymers warrant further investigation as a potential clinical treatment for hemorrhagic shock and possibly other microcirculatory disorders.     

New Insights into the Microvascular Mechanisms of Drag Reducing Polymers: Effect on the Cell-Free Layer

Drag-reducing polymers (DRPs) significantly increase blood flow, tissue perfusion, and tissue oxygenation in various animal models. In rectangular channel microfluidic systems, DRPs were found to significantly reduce the near-wall cell-free layer (CFL) as well as modify traffic of red blood cells (RBC) into microchannel branches. In the current study we further investigated the mechanism by which DRP enhances microvascular perfusion. We studied the effect of various concentrations of DRP on RBC distribution in more relevant round microchannels and the effect of DRP on CFL in the rat cremaster muscle in vivo. In round microchannels hematocrit was measured in parent and daughter branch at baseline and after addition of DRP. At DRP concentrations of 5 and 10 ppm, the plasma skimming effect in the daughter branch was eliminated, as parent and daughter branch hematocrit were equivalent, compared to a significantly lowered hematocrit in the daughter branch without DRPs. In anesthetized rats (N=11) CFL was measured in the cremaster muscle tissue in arterioles with a diameter of 32.6 ± 1.7 µm. In the control group (saline, N=6) there was a significant increase in CFL in time compared to corresponding baseline. Addition of DRP at 1 ppm (N=5) reduced CFL significantly compared to corresponding baseline and the control group. After DRP administration the CFL reduced to about 85% of baseline at 5, 15, 25 and 35 minutes after DRP infusion was complete. These in vivo and in vitro findings demonstrate that DRPs induce a reduction in CFL width and plasma skimming in the microvasculature. This may lead to an increase of RBC flux into the capillary bed, and thus explain previous observations of a DRP mediated enhancement of capillary perfusion.     

Improvement of the microcirculation in the acute ischemic rat limb during intravenous infusion of drag-reducing polymers

Drag-reducing polymers (DRPs) are blood-soluble macromolecules that can increase blood flow and reduce vascular resistance. The purpose of the present study is to examine the effects of DRPs on microcirculation in rat hind limb during acute femoral artery occlusion. Two groups of 20 male Wistar rats were subjected to either hemodynamic measurement or contrast enhanced ultrasound (CEU) imaging during peripheral ischemia. Both groups were further subdivided into a DRP-treated group or a saline-treated group. Polyethylene oxide (PEO) was chosen as the test DRP, and rats were injected with either 10 ppm PEO solution or saline through the caudal vein at a constant rate of 5 ml/h for 20 min. Abdominal aortic flow, iliac artery pressure, iliac vein pressure, heart rate, carotid artery pressure and central venous pressure (CVP) were monitored, and vascular resistance was calculated by (iliac artery pressure-iliac vein pressure)/abdominal aortic blood flow. Flow perfusion and capillary volume of skeletal muscle were measured by CEU. During PEO infusion, abdominal aortic blood flow increased (p<0.001) and vascular resistance decreased (p<0.001) compared to rats that received saline during peripheral ischemia. There was no significant change in ischemic skeletal capillary volume (A) with DRP treatment (p>0.05), but red blood cell velocity (β) and capillary blood flow (A×β) increased significantly (p<0.05) during PEO infusion. In addition, A, β and A×β all increased (p<0.05) in the contralateral hind limb muscle. In contrast, PEO had no significant influence on heart rate, mean carotid artery blood pressure or CVP. Intravenous infusion of drag reducing polymers may offer a novel hydrodynamic approach for improving microcirculation during acute peripheral ischemia.     

Drag-reducing polymers diminish near-wall concentration of platelets in microchannel blood flow

The accumulation of platelets near the blood vessel wall or artificial surface is an important factor in the cascade of events responsible for coagulation and/or thrombosis. In small blood vessels and flow channels this phenomenon has been attributed to the blood phase separation that creates a red blood cell (RBC)-poor layer near the wall. We hypothesized that blood soluble drag-reducing polymers (DRP), which were previously shown to lessen the near-wall RBC depletion layer in small channels, may consequently reduce the near-wall platelet excess. This study investigated the effects of DRP on the lateral distribution of platelet-sized fluorescent particles (diam. = 2 μm, 2.5 × 10?/ml) in a glass square microchannel (width and depth = 100 μm). RBC suspensions in PBS were mixed with particles and driven through the microchannel at flow rates of 6-18 ml/h with and without added DRP (10 ppm of PEO, MW = 4500 kDa). Microscopic flow visualization revealed an elevated concentration of particles in the near-wall region for the control samples at all tested flow rates (between 2.4 ± 0.8 times at 6 ml/h and 3.3 ± 0.3 times at 18 ml/h). The addition of a minute concentration of DRP virtually eliminated the near-wall particle excess, effectively resulting in their even distribution across the channel, suggesting a potentially significant role of DRP in managing and mitigating thrombosis.     

Differential Roles of Arabidopsis Dynamin-Related Proteins DRP3A,DRP3B,and DRP5B in Organelle Division

Dynamin-related proteins (DRPs) are key components of the organelle division machineries, functioning as molecular scissors during the fission process. In Arabidopsis, DRP3A and DRP3B are shared by peroxisomal and mitochondrial division, whereas the structurally-distinct DRP5B (ARC5) protein is involved in the division of chloroplasts and peroxisomes. Here, we further investigated the roles of DRP3A, DRP3B, and DRP5B in organelle division and plant development. Despite DRP5B's lack of stable association with mitochondria, drp5B mutants show defects in mitochondrial division. The drp3A-2 drp3B-2 drp5B-2 triple mutant exhibits enhanced mitochondrial division phenotypes over drp3A-2 drp3B-2, but its peroxisomal morphology and plant growth phenotypes resemble those of the double mutant. We further demonstrated that DRP3A and DRP3B form a supercomplex in vivo, in which DRP3A is the major component, yet DRP5B is not a constituent of this complex. We thus conclude that DRP5B participates in the division of three types of organelles in Arabidopsis, acting independently of the DRP3 complex. Our findings will help elucidate the precise composition of the DRP3 complex at organelle division sites, and will be instrumental to studies aimed at understanding how the same protein mediates the morphogenesis of distinct organelles that are linked by metabolism.     

Presynaptic facilitatory action of locus coeruleus stimulation upon hindlimb sensory impulse transmission in decerebrate cats

This study sought to delineate the presynaptic role of the locus coeruleus (LC) on hindlimb primary afferent terminals. Changes in presynaptic function in response to LC stimulation were assessed by measuring the dorsal root potential (DRP), interaction of LC- and peripherally-evoked DRPs, and intraspinal afferent terminal excitability. LC stimulation in unanesthetized, decerebrate cats produced a sequence of early and late positive DRPs succeeded by a small-sized negative DRP. Conditioning the negative DRPs elicited from individual hindlimb nerve branches with LC stimuli led to a decrease in test DRPs. Similarly, there was a predominant decrease in excitability in both large muscle and cutaneous afferent terminals. These data suggest a presynaptic role of the LC in augmenting afferent impulse transmission, presumably through inhibition of tonically active interneurons having axoaxonic contacts on primary afferents; functionally, presynaptic facilitation.     

Drug-Related Problems in Patients with Benign Prostatic Hyperplasia: A Cross Sectional Retrospective Study

Benign Prostatic Hyperplasia (BPH) patients are at risk of acquiring drug-related problems (DRPs), as it is present in the majority of aging men. To date, DRPs among BPH patients have not been well studied. We conducted this retrospective study in a tertiary hospital in Malaysia from January 2009 to June 2012 with the aim of identifying the factors associated with DRPs among BPH patients. The Pharmaceutical Care Network Europe Classification Version (PCNE) 5.01 was used as a tool to classify DRPs. We enrolled 203 patients from 259 hospital admissions. A total of 390 DRPs were found and there was an average of 1.5±1.3 problems per hospitalization. 76.1% of hospital admissions included at least one DRP. The most common DRP categories encountered were drug choice problems (45.9%), drug interactions (24.9%), and dosing problems (13.3%). Factors such as advanced age (p = 0.005), a hospital stay of more than 6 days (p = 0.001), polydrug treatments (p<0.001), multiple comorbidities (p<0.001), and comorbid cardiovascular disease (p = 0.011), diabetes mellitus(p = 0.001), hypertension (p<0.001) and renal impairment (p = 0.011) were significantly associated with the occurrence of DRPs. These data indicated that the prevalence of DRPs is high among BPH patients. The identification of different subtypes of DRPs and the factors associated with DRPs may facilitate risk reduction for BPH patients.     

A dynamin-related protein required for nuclear remodeling in Tetrahymena

Dynamin-related proteins (DRPs) are GTPases that reversibly assemble on cellular membranes [1]. Individual DRPs (here "DRP" includes authentic dynamins) function in fission or tubulation of the plasma membrane, trans-Golgi network, mitochondria, peroxisomes, chloroplasts, and endosomes [1] and in mitochondrial fusion [2]. Many of these functions are widespread; they are present in animals, plants, trypanosomes, Giardia, ciliates, alga, and slime molds [3-8]. Lineage-specific expansions of the gene family created specialized DRPs. In animals, such DRPs include MxB, which has been reported to regulate nuclear-pore transport [9]. Whereas many unicellular organisms possess a small number of DRPs, expansions occurred in some protist lineages. The eight DRPs in the ciliate Tetrahymena thermophila might contribute to aspects of ciliate complexity. Each ciliate cell contains distinct germline and somatic nuclei, whose differentiation and maintenance must require distinct machinery [10, 11]. Here we show that Drp6p, previously shown to be targeted to the nuclear envelope [3], is required for macronuclear development. Drp6p activity, which is distinct from that of the only other known nuclear DRP, is modulated by a combination of stage-specific subcellular targeting and assembly dynamics. This work demonstrates a novel DRP activity and presents a system in which environmental and developmental cues can be used for manipulating key aspects of regulation.     

The Arabidopsis Chloroplast Division Protein DYNAMIN-RELATED PROTEIN5B Also Mediates Peroxisome Division

Peroxisomes are highly dynamic organelles involved in various metabolic pathways. The division of peroxisomes is regulated by factors such as the PEROXIN11 (PEX11) proteins that promote peroxisome elongation and the dynamin-related proteins (DRPs) and FISSION1 (FIS1) proteins that function together to mediate organelle fission. In Arabidopsis thaliana, DRP3A/DRP3B and FIS1A (BIGYIN)/FIS1B are two pairs of homologous proteins known to function in both peroxisomal and mitochondrial division. Here, we report that DRP5B, a DRP distantly related to the DRP3s and originally identified as a chloroplast division protein, also contributes to peroxisome division. DRP5B localizes to both peroxisomes and chloroplasts. Mutations in the DRP5B gene lead to peroxisome division defects and compromised peroxisome functions. Using coimmunoprecipitation and bimolecular fluorescence complementation assays, we further demonstrate that DRP5B can interact or form a complex with itself and with DRP3A, DRP3B, FIS1A, and most of the Arabidopsis PEX11 isoforms. Our data suggest that, in contrast with DRP3A and DRP3B, whose orthologs exist across plant, fungal, and animal kingdoms, DRP5B is a plant/algal invention to facilitate the division of their organelles (i.e., chloroplasts and peroxisomes). In addition, our results support the notion that proteins involved in the early (elongation) and late (fission) stages of peroxisome division may act cooperatively.     

POLY(HPMA)-COATED LIPOSOMES DEMONSTRATE PROLONGED CIRCULATION IN MICE

Surface modification of liposomes with amphiphilic flexible polymers significantly prolongs their circulation time in blood and reduces uptake by cells of the reticuloendothelial system (RES). Several polymers have already been shown to provide steric protection to liposomes. Still more polymers are expected to serve this purpose, thus broadening the variability of properties of long-circulating liposomes. Poly[N-(2-hydroxypropyl)methacrylamide] (poly (HPMA)) seems to have some properties similar to polyethylene glycol (PEG), the most widely used polymer in liposome surface modification, including flexibility, hydrophilicity and low immunogenicity, which suggest that it may also function as an efficient steric protector of liposomes. Semitelechelic poly(HPMA) with single- or double-oleic acid hydrophobic terminus were synthesized and incorporated into the surface of liposomes composed of phosphatidylcholine and cholesterol. These poly(HPMA)-modified liposomes provided strong steric protection for liposomes, increasing their circulation time and decreasing liver accumulation in experimental mice. Poly(HPMA)-modified liposomes may become a useful addition to a family of long-circulating liposomes with potential to be used as a drug delivery system.     

Ciliate biology: dynamin goes nuclear

Dynamin and dynamin-related proteins (DRPs) mediate an array of membrane fission processes. A Tetrahymena DRP has adopted a new role, assisting in nuclear differentiation, a finding that further highlights these proteins - and this ciliate - as biological innovators.     

Separan AP-273 and renal function: a novel natriuretic substance

Recent studies have demonstrated that an anionic polyacrylamide (Separan, Union Carbide Corp.) decreased the formation of atherosclerotic lesions in the rabbit (Separan AP-30) and increased cardiac output (Separan AP-273) in the rat. Since the effect of these compounds on renal function was unknown, we investigated the dose-response relationship between Separan AP-273 and the renal excretion of electrolytes and water. In the anesthetized rat, intravenous injections of Separan at 0.01, 0.03, 0,10, and 0.30 mg/kg produced a dose-related increase in urine volume, sodium excretion, and osmolar clearance. Potassium excretion was increased less than twofold only at the maximal dose tested. At this high dose, the effect on sodium and water excretion was greater (five- and seven-fold, respectively). Creatinine clearance was not altered by these interventions. As well, the maximal dose studied was previously shown to have no effect on blood flow. These results indicate that Separan AP-273 is a potent diuretic and natriuretic substance. Taken together with similar studies using the poly(ethylene oxide) Polyox WSR N-60K, these results suggest that drag-reducing polymers may represent a novel group of compounds with diuretic and natriuretic effects.     

Neurochemical and ionic mechanisms of dorsal root potentials in the spinal cord of immature rats

Dorsal root potentials (DRPs) were recorded by a sucrose gap method in experiments on parasagittal slices of the isolated rat spinal cord. In most cases the DRP consisted of fast and slow waves. The fast wave of DRP was inhibited by the GABA antagonist picrotoxin and the blocker of GABA-activated chloride channels, furosemide, but it was potentiated by pentobarbital sodium. The slow wave of DRP disappeared if the extracellular K⁺ concentration was raised to 10 mM and it was depressed by tetraethylammonium and 4-aminopyridine, blockers of electrically excitable potassium channels. It is concluded that the fast wave of DRP and the initial components of the slow wave of DRP are GABA-ergic in origin; the slow wave of DRP, however, is linked with an increase in extracellular K⁺ concentration near the primary afferent terminals. The possible mechanisms of the increase in extracellular K⁺ concentration during dorsal root stimulation are discussed.A. M. Gor'kii Donetsk Medical Institute. Translated from Neirofiziologiya, Vol. 16, No. 6, pp. 796–800, November–December, 1984.     

The control of peroxisome number and size during division and proliferation

Like other subcellular organelles, peroxisomes divide and segregate to daughter cells during cell division, but this organelle can also proliferate or be degraded in response to environmental cues. Although the mechanisms and genes involved in these processes are still under active investigation, an important player in peroxisome proliferation is a dynamin-related protein (DRP) that is recruited to the organelle membrane by a DRP receptor. Related DRPs also function in the division of mitochondria and chloroplasts. Many other proteins and signals regulate peroxisome division and proliferation, but their modes of action are still being studied.     

Poly(fumaric-co-sebacic) microspheres as oral drug delivery systems

The current study focuses on the development of bioadhesive oral delivery systems based on bioerodible polyanhydrides. The polymers were studied and characterized using a novel tensiometer based on a very sensitive electrobalance. The system was designed to mimic in vivo interactions, thus all experiments were conducted with freshly excised tissue immersed in physiological saline at 37 degrees C. Poly(fumaric-co-sebacic) [P(FA:SA)] was found to be the most bioadhesive polymer from a series of different thermoplastic materials evaluated. Correlation with in vivo performance was investigated by determining gastrointestinal (GI) residence time of barium-loaded microspheres. Residence times of 24 to 36 h provided a strong indication that these microspheres were good candidates for bioadhesive drug delivery systems. To evaluate the effect of these materials on bioavailability, the anticoagulant drug, dicumarol, was encapsulated. Systemic blood levels demonstrated increased bioavailability for the encapsulated dicumarol formulation as compared with unencapsulated drug. (c) 1996 John Wiley & Sons, Inc.     

Arabidopsis ELONGATED MITOCHONDRIA1 is required for localization of DYNAMIN-RELATED PROTEIN3A to mitochondrial fission sites

Mitochondrial fission is achieved partially by the activity of self-assembling dynamin-related proteins (DRPs) in diverse organisms. Mitochondrial fission in Arabidopsis thaliana is mediated by DRP3A and DRP3B, but the other genes and molecular mechanisms involved have yet to be elucidated. To identify these genes, we screened and analyzed Arabidopsis mutants with longer and fewer mitochondria than those of the wild type. ELM1 was found to be responsible for the phenotype of elongated mitochondria. This phenotype was also observed in drp3a plants. EST and genomic sequences similar to ELM1 were found in seed plants but not in other eukaryotes. ELM1:green fluorescent protein (GFP) was found to surround mitochondria, and ELM1 interacts with both DPR3A and DRP3B. In the elm1 mutant, DRP3A:GFP was observed in the cytosol, whereas in wild-type Arabidopsis, DRP3A:GFP localized to the ends and constricted sites of mitochondria. These results collectively suggest that mitochondrial fission in Arabidopsis is mediated by the plant-specific factor ELM1, which is required for the relocalization of DRP3A (and possibly also DRP3B) from the cytosol to mitochondrial fission sites.     

Blood clearance and biodistribution of polymer brush-afforded silica particles prepared by surface-initiated living radical polymerization

The physiological properties of polymer brush-afforded silica particles prepared by surface-initiated living radical polymerization were investigated in terms of the circulation lifetime in the blood and distribution in tissues. Hydrophilic polymers consisting mainly of poly(poly(ethylene glycol) methyl ether methacrylate) were grafted onto silica particles by surface-initiated atom transfer radical polymerization that was mediated by a copper complex to produce hairy hybrid particles. A series of hybrid particles was synthesized by varying the diameter of the silica core and the chain length of the polymer brush to examine the relationship between their physicochemical and physiological properties. The hybrid particles were injected intravenously into mice to investigate systematically their blood clearance and body distribution. It was revealed that the structural features of the hybrid particles significantly affected their in vivo pharmacokinetics. Some hybrid particles exhibited an excellently prolonged circulation lifetime in the blood with a half life of ～20 h. When such hybrid particles were injected intravenously into a tumor-bearing mouse, they preferentially accumulated in tumor tissue. The tumor-targeted delivery was optically visualized using hybrid particles grafted with fluorescence-labeled polymer brushes.     

Dnm1 forms spirals that are structurally tailored to fit mitochondria

Dynamin-related proteins (DRPs) are large self-assembling GTPases whose common function is to regulate membrane dynamics in a variety of cellular processes. Dnm1, which is a yeast DRP (Drp1/Dlp1 in humans), is required for mitochondrial division, but its mechanism is unknown. We provide evidence that Dnm1 likely functions through self-assembly to drive the membrane constriction event that is associated with mitochondrial division. Two regulatory features of Dnm1 self-assembly were also identified. Dnm1 self-assembly proceeded through a rate-limiting nucleation step, and nucleotide hydrolysis by assembled Dnm1 structures was highly cooperative with respect to GTP. Dnm1 formed extended spirals, which possessed diameters greater than those of dynamin-1 spirals but whose sizes, remarkably, were equal to those of mitochondrial constriction sites in vivo. These data suggest that Dnm1 has evolved to form structures that fit the dimensions of mitochondria.