Low molecular weight heparins in special populations

Low molecular weight heparins (LMWH) are replacing unfractionated heparin (UH) as safe and effective agents for the prevention and treatment of thromboembolism. Although LMWH offer many advantages over UH, usage is less clearly defined in certain special populations, including renal dysfunction, obesity and pregnancy. This article will briefly review the pharmacology of LMWH and discuss usage in these special populations.     

Low molecular weight heparins: a valuable tool in the treatment of acute coronary syndromes

Standard heparin, low molecular weight heparin and aspirin are at present the only antithrombotic agents of proven value in the initial treatment of patients with an acute coronary syndrome. The combined use of aspirin and one of the heparins for at least 6 days should be considered for all such patients. With their high bio-availability after subcutaneous injection and prolonged half-life, low molecular weight heparins simplify short-term treatment in the acute phase and enable long-term therapy to be maintained on an outpatient basis without the need for repeated laboratory monitoring of anticoagulant effects. Such long-term therapy would appear to be beneficial, at least in high-risk patients, in the light of increasing evidence that the underlying lesion in acute coronary syndromes resolves over a period of weeks or months.     

Low molecular weight heparin

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Differential interactions of heparin and heparan sulfate glycosaminoglycans with the selectins. Implications for the use of unfractionated and low molecular weight heparins as therapeutic agents

The selectins are calcium-dependent C-type lectins that bind certain sialylated, fucosylated, sulfated glycoprotein ligands. L-selectin also recognizes endothelial proteoglycans in a calcium-dependent manner, via heparan sulfate (HS) glycosaminoglycan chains enriched in unsubstituted glucosamine units. We now show that these HS chains can also bind P-selectin, but not E-selectin. However, while L-selectin binding requires micromolar levels of free calcium, P-selectin recognition is largely divalent cation-independent. Despite this, HS chains bound to P-selectin are eluted by ethylenediamine tetraacetic acid (EDTA), but only at high concentrations. Porcine intestinal mucosal (mast cell-derived) heparin (PIM-heparin) shows similar properties, with no binding to E-selectin, calcium-dependent binding of a subfraction to L-selectin and to P-selectin, and calcium-independent binding of a larger fraction to P-selectin, the latter being disrupted by high EDTA concentrations. Analysis of defined heparin fragment pools shows a size dependence for interaction, with tetradecasaccharides showing easily detectable binding to L- and P-selectin affinity columns. L-selectin binding fragments include more heavily sulfated and epimerized regions and, as with the endothelial HS chains, they are enriched in free amino groups. The P-selectin binding component includes this fraction as well as some less highly modified regions. Thus, endothelium-derived HS chains and mast cell-derived heparins could play a role in modulating the biology of selectins in vivo. Notably, P- and L-selectin binding to sialyl-Lewisx and to HL-60 cells (which are known to carry the native ligand PSGL-1) is inhibited by unfractionated pharmaceutical heparin preparations at concentrations 12-50-fold lower than those recommended for effective anticoagulation in vivo. In contrast, two low molecular weight heparins currently considered as clinical replacements for unfractionated heparin are much poorer inhibitors. Thus, patients undergoing heparin therapy for other reasons may be experiencing clinically significant inhibition of L- and P-selectin function, and the current switchover to low-molecular weight heparins may come at some loss of this effect. Low-dose unfractionated heparin should be investigated as a treatment option for acute and chronic diseases in which P- and L-selectin play pathological roles.     

Recent clinical trials in the treatment of venous thromboembolism and unstable angina with low molecular weight heparins

STUDY OBJECTIVE: To determine the effects of introduction of a new monitoring system for fluid absorption during transurethral resection of the prostate (TURP) using an irrigating solution containing 0.5% alcohol. STUDY DESIGN: Prospective clinical investigation, with implementation of statistical process control. SETTING: Inpatients for TURP at a major non-university teaching hospital. PATIENTS: 312 male ASA physical status I, II, III, and IV patients scheduled for TURP. INTERVENTIONS: Intraoperative breath alcohol levels were measured for detection of fluid absorption. MEASUREMENTS AND MAIN RESULTS: Calculation of the amount of fluid absorbed using measured breath alcohol values. Process variability (i.e., numbers of patients with significant fluid absorption) was defined by statistical process control tools. No trend change of prevalence of fluid absorption was noted until 150 procedures had been completed. Reduction of prevalence of significant fluid absorption was noted and no patients were treated postoperatively in the intensive care unit. No relevant side effects were seen in patients with significant fluid absorption. No mortality and no severe clinical morbidity was seen after the introduction of the new monitoring. CONCLUSION: Using an irrigating fluid marked with 0.5% ethanol resulted in a decreased prevalence of fluid absorption over time.     

Low molecular weight dermatan sulfate as an antithrombotic agent. Structure-activity relationship studies

A structure-activity relationship of low molecular weight dermatan sulfate was undertaken to understand better this new non-heparin, glycosaminoglycan-based antithrombotic agent. A dermatan sulfate prepared from bovine intestinal mucosa [average molecular weight (MWavg) 25,000], and currently in clinical trials as an antithrombotic agent, was used in this study. Dermatan sulfate was partially depolymerized using hydrogen peroxide and copper(II) as catalyst to MWavg 5600 to obtain a low molecular weight dermatan sulfate. This low molecular weight dermatan sulfate was then fractionated by gel permeation chromatography to obtain four subfractions having MWavg 7800, 5500, 4200 and 1950. The dermatan sulfate, low molecular weight dermatan sulfate and its subfractions showed substantially different optical rotations. The 1H-NMR spectroscopic analysis of dermatan sulfate samples showed some differences including increased content of GalpNAc4S6S residues and improved resolution in ring resonances for low molecular weight dermatan sulfate fractions, primarily the result of reduced molecular weight and lowered heterogeneity. Saccharide compositional analysis relied on chondroitin ABC lyase treatment followed by capillary electrophoresis. Polyacrylamide gel-based oligosaccharide mapping was also performed by treating dermatan sulfate samples with chondroitin B, AC and ABC lysases. These analyses showed increased amounts of sulfation as the MWavg decreased. In vitro bioassay showed maximum anti-Xa activity in the 4.2 kDa fraction and maximum heparin cofactor II-mediated anti-IIa activity in the 5.5 kDa fraction. The in vivo antithrombotic activity of these fractions was measured using a modified Wessler stasis thrombosis model. The 4.2 kDa fraction showed greater antithrombotic activity than the other low molecular weight dermatan sulfate fractions, dermatan sulfate, and low molecular weight dermatan sulfate. This enhanced activity may result from several structural features of the 4.2 kDa fraction including: a high content of 4,6- and 2,4-disulfated disaccharide sequences; the requirement of specific chain length; a change in the ratio of iduronic to glucuronic acid; and the presence of chondroitin ABC lyase resistant material.     

Low molecular weight GTP-binding proteins are altered in platelet hyperaggregation in IDDM

We examined the hypothesis that hyperaggregating platelets from patients with insulin dependent diabetes mellitus (IDDM) have an alteration in location and function of the guanine nucleotide (GTP)-binding proteins. Platelets from 10 IDDM and 12 age-matched healthy control subjects were collected and washed. Thrombin-induced platelet aggregation (0.025 and 0.05 units for 60 seconds) was increased in IDDM (8.3 +/- 1.8% vs 22.3 +/- 4.4%, P < .05 and 49.9 +/- 7.3% vs 70.9 +/- 7.0%, P < .05). Four small molecular weight GTP-binding proteins were identified by binding of [32P]-GTP on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) in the cytosol and membranes of these platelets. Each showed specificity for binding [32P]-GTP by competitive inhibition with unlabeled GTP. The total of the 27/28 kDa proteins was decreased in the membrane fraction (414 +/- 30 vs 252 +/- 40 dpm micrograms-1 protein x min, P < .05) and increased in the cytosolic fraction (62 +/- 8 vs 129 +/- 21 dpm unit-1 LDH x min, P < .05) in IDDM. The 21 kDa protein (60.3 +/- 3.5 vs 45.4 +/- 2.9 dpm micrograms-1 protein x min, P < .05) was decreased in platelet membrane in persons with IDDM. In conclusion, increased platelet aggregation in IDDM is accompanied by an altered cellular distribution of a 27/28 kDa GTP-binding protein. These data suggest that the low molecular weight GTP-binding proteins of the 27/28 kDa range may play an important regulatory role in the hyperaggregatory platelets in diabetes.     

Low molecular weight heparin: a critical analysis of clinical trials

LMWHs are an important new class of antithrombotic agents. They differ from UFH in having relatively more anti-Xa activity, greater bioavailability at low doses, longer half-life, and more predictable anticoagulant response when administered in fixed doses. These properties allow LMWHs to be administered QD or at most BID and without laboratory monitoring. The incidence of heparin-induced thrombocytopenia also appears to be lower with an LMWH than with heparin. Given their favorable pharmacological profile, it was of interest to critically appraise clinical trials of thromboprophylaxis and treatment with these new agents. In orthopedic trials, it was noted that LMWH provided safe and effective thromboprophylaxis for patients undergoing major orthopedic surgery of the lower limb. In those having hip arthroplasty, LMWH was as effective as low-intensity warfarin therapy, but its use was associated with more wound hematomas. In those having total knee arthroplasty, LMWH was more effective than warfarin and did not increase bleeding. However, the prevalence of DVTs complicating this procedure as well as acute hip fracture remains unacceptably high, and additional studies of LMWH in combination with other prophylactic methods, such as external pneumatic compression, are needed. Only one adequately designed trial found less bleeding resulted from LMWH prophylaxis administered at an equivalent antithrombotic dose to UFH. In general medical patients, LMWH appeared to be as effective as UFH and had the advantages of less frequent injections and fewer injection site hematomas. In general surgical patients, there was a lower risk of thromboembolism but a trend toward an increase in bleeding events. Subjects with strokes and spinal cord injuries benefited from fewer thrombotic events, and the latter had fewer bleeding complications. Other potential indications for LMWH, such as cardiopulmonary bypass, hemodialysis, and preservation of graft patency, are presently under study. Perhaps the most impressive benefits of LMWH will be realized when it is used for the treatment of venous thromboembolism. The meta-analysis presented in this review showed a trend toward greater efficacy with LMWH and fewer major bleeding events in comparison with adjusted-dose intravenous UFH. Also, during the months following the thrombotic event, there was significantly less mortality in patients receiving LMWH. A further advantage was the subcutaneous route of administration and lack of requirement for laboratory monitoring. Additional treatment trials are presently in progress and may establish LMWH as the treatment of choice for patients with thromboembolic disorders.     

Low molecular weight Cooperia oncophora antigens. Potential to discriminate between susceptible and resistant calves after infection

The recognition of low molecular weight proteins by sera obtained during a single oral (primary) infection with 100,000 3rd-stage Cooperia oncophora larvae was studied in calves. Three groups of 6 or 7 calves were selected based on different egg excretion patterns. SDS-gel electrophoresis of adult Cooperia antigen under reducing conditions, followed by Western blotting, revealed that resistance of individual calves to C. oncophora might be related with antibody responses (42 days post infection) against at least 2 protein fragments (14-16 kDa and 27 kDa). The 14-16-kDa protein complex was bound, to some extent, by individual sera from all calves. The intensity of staining was negatively correlated with egg excretion on Day 42 p.i. Calves with high egg counts on Day 21 p.i. either did not or only weakly recognized the 27-kDa band. It has to be established whether the 14-16 kDa (or recombinant 14.2 kDa) provides a tool for immunodiagnostics and whether the 27-kDa fragment can help further unravel immune-mediated resistance to Cooperia.     

Low molecular weight silicones are widely distributed after a single subcutaneous injection in mice

To examine the distribution of low molecular weight silicones in body organs, separate groups of female CD-1 mice were injected with either breast implant distillate composed primarily of hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, and tetradecamethylcycloheptasiloxane or a polydimethylsiloxane oil containing low molecular weight linear siloxanes. Mice were injected subcutaneously in the suprascapular area and killed at different times. Levels of individual low molecular weight silicones were measured in 10 different organs (brain, heart, kidney, liver, lung, mesenteric lymph nodes, ovaries, spleen, skeletal muscle, and uterus). In mice treated with the cyclosiloxane mixture and killed at 3, 6, or 9 weeks, highest levels of cyclosiloxanes were found in the mesenteric lymph nodes, ovaries, and uterus, but all organs examined contained cyclosiloxanes. In a cohort killed at 1 year, most organs contained measurable cyclosiloxanes with highest levels in mesenteric lymph nodes, abdominal fat, and ovaries. Of the individual cyclosiloxanes measured, selective retention of decamethylcyclopentasiloxane and dodecamethylcyclohexasiloxane relative to octamethylcyclotetrasiloxane was seen in all organs at all time points studied. Organs from animals receiving the linear siloxane mixture were harvested at 9, 12, and 15 weeks. We found maximum levels in the brain, lungs, and mesenteric lymph nodes, but all other organs contained measurable levels. These data are, to the best of our knowledge, the first demonstration that after a single subcutaneous injection silicones are widely distributed throughout the body and can persist over an extended period.     

Low birth weight and ventricular enlargement in a high-risk sample.

Studied the relation between adult ventricle size and perinatal complications and birth weight using Ss from a Danish high-risk sample previously studied by 2 of the present authors (1965) in a longitudinal study of children and subsequently diagnosed in a study by F. Endicott and R. Spitzer (1972). Of the 58 28–37 yr olds available for the present study, 15 had been diagnosed as schizophrenic, 18 as borderline, and 25 as having no mental illness. 10 schizophrenics, 10 borderlines, and 14 normals were given computerized tomography scans. Results show ventricular enlargement was significantly negatively related to length and weight at birth and to midwife ratings of neonate prematurity. A lack of association was found between ventricle brain ration (VBR) and composite complication score. Results suggest that enlarged ventricles might be associated with insults occurring in utero. The possibility that a fetal viral infection caused CNS system damage and consequent atrophy as measured by VBR is hypothesized. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A new chronometric assay to determine plasma antifactor Xa activity which is insensitive to the antithrombin activity of low molecular weight heparins

Some commercially available chronometric assays are influenced by the residual antithrombin activity of low molecular weight heparins (LMWH) and they underestimate the ex vivo anti Xa activity. We have evaluated a new kit (Staclot-Heparin) highly specific for the anti Xa activity of LMWH. A comparison with the results given by a reference chromogenic method (Stachrom-Heparin) indicates a very good correlation between the 2 assays (r = 0.95, n = 59). This new assay is not influenced by vitamin K antagonist treatments. Clinical biologists now have the possibility of determining the anti Xa activity generated by LMWH easily and accurately, using a chronometric assay.     

Low molecular weight viral RNAs transcribed by RNA polymerase III during adenovirus 2 infection

Nuclei isolated from human cells productively infected with adenovirus 2 have been shown to synthesize four low molecular weight RNA species which hybridize efficiently to viral DNA. One species corresponds to the 5.5S or VA RNA (Ohe, Weissman, and Cooke, 1969), and is designated V156. The other three species are novel and have been designated V200, V140, V130, since they are approximately 200, 140, and 130 nucleotides in length, respectively. These viral RNAs retain their distinct electrophoretic properties after denaturation with formamide. RNA species with electrophoretic mobilities similar to those of the V200, V156, and V140 RNAs have been found in the cytoplasmic fraction of cells at late times after adenovirus infection. In isolated nuclei, the V200, V156, V140, and V130 RNAs are all synthesized by DNA-dependent RNA polymerase III, since synthesis is sensitive to high but not to low concentrations of alpha-amanitin. The synthesis of these low molecular weight RNAs continues for a prolonged period of time in isolated nuclei, suggesting that reinitiation occurs. Adenovirus 2 DNA fragments obtained by digestion with restriction endonucleases Eco RI and Sma I were used to map the location of the DNA sequences which encode the RNAs. All the low molecular weight RNAs hybridized to a region of the genome between o.18 and 0.38 fractional lengths from the left end of the adenovirus genome, suggesting that the respective DNA sequences are clustered. Other nonviral low molecular weight RNAs are synthesized in nuclei isolated from infected cells. These include the cellular 5S rRNA species which was minitored by its hybridization to purified 5S DNA from Xenopus laevis.     

Impaired neuroendocrine response mediates refractoriness to cardiopulmonary resuscitation in spinal anesthesia

The authors hypothesized that excessive reassurance-seeking would prospectively predict changes in depressive symptoms, even controlling for changes in anxious symptoms, and would not predict changes in anxious symptoms controlling for changes in depressive symptoms. This prediction was supported in a study of 1,005 air force cadets. Participants completed measures of excessive reassurance-seeking and depressive and anxious symptoms before basic training, and completed symptom measures again following basic training. This study, together with others, demonstrates that excessive reassurance-seeking is an important depression-related variable that deserves serious attention as a potential vulnerability factor.