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Biomedical subjects

R F Jacob

Publications and source records attributed to R F Jacob.

At least 19 recordsLinked to original sources
PubMed2001

Evidence for distinct cholesterol domains in fiber cell membranes from cataractous human lenses.

Previous studies in our laboratory have provided direct evidence for the existence of distinct cholesterol domains within the plasma membranes of human ocular lens fiber cells. The fiber cell plasma membrane is unique in that it contains unusually high concentrations of cholesterol, with cholesterol to phospholipid (C/P) mole ratios ranging from 1 to 4. Since membrane cholesterol content is disturbed in the development of cataracts, it was hypothesized that perturbation of cholesterol domain structure occurs in cataracts. In this study, fiber cell plasma membranes were isolated from both normal (control) and cataractous lenses and assayed for cholesterol and phospholipid. Control and cataractous whole lens membranes had C/P mole ratios of 3.1 and 1.7, respectively. Small angle x-ray diffraction approaches were used to directly examine the structural organization of the cataractous lens plasma membrane versus control. Both normal and cataractous oriented membranes yielded meridional diffraction peaks corresponding to a unit cell periodicity of 34.0 A, consistent with the presence of immiscible cholesterol domains. However, comparison of diffraction patterns indicated that cataractous lens membranes contained more pronounced and better defined cholesterol domains than controls, over a broad range of temperature (5-40 degrees C) and relative humidity (52-92%) levels. In addition, diffraction analyses of the sterol-poor regions of cataractous membranes indicated increased membrane rigidity as compared with control membranes. Modification of the membrane lipid environment, such as by oxidative insult, is believed to be one potential mechanism for the formation of highly resolved cholesterol domains despite significantly reduced cholesterol content. The results of this x-ray diffraction study provide evidence for fundamental changes in the lens fiber cell plasma membrane structure in cataracts, including the presence of more prominent and highly ordered, immiscible cholesterol domains.

Aged↗
PubMed2000

Antioxidant activity of the monoamine oxidase B inhibitor lazabemide.

Free radical-induced damage to lipid and protein constituents of neuronal membranes contributes to the pathophysiology of neurodegenerative diseases, including Alzheimer's disease (AD). The development of an effective inhibitor of oxidative stress represents an important goal for the treatment of AD. In this study, the intrinsic antioxidant activity of lazabemide, a potent and reversible inhibitor of monoamine oxidase B (MAO-B), was tested in a membrane-based model of oxidative stress. Under physiologic-like conditions, lazabemide inhibited lipid peroxidation in a highly concentration-dependent manner. At low, pharmacologic levels of lazabemide (100.0 nM), there was a significant (P < 0.001) and catalytic reduction in lipid peroxide formation, as compared with control samples. The antioxidant activity of lazabemide was significantly more effective than that of either vitamin E or the MAO-B inhibitor, selegiline. The ability of lazabemide to inhibit oxidative damage is attributed to physico-chemical interactions with the membrane lipid bilayer, as determined by small angle x-ray diffraction methods. By partitioning into the membrane hydrocarbon core, lazabemide can inhibit the propagation of free radicals by electron-donating and resonance-stabilization mechanisms. These findings indicate that lazabemide is a potent and concentration-dependent inhibitor of membrane oxy-radical damage as a result of inhibiting membrane lipid peroxidation, independent of MAO-B interactions.

Animals↗
PubMed2000

Hierarchy of research design used to categorize the "strength of evidence" in answering clinical dental questions.

The purpose of this article is to highlight important features of research design that clinicians can use to determine which articles are useful when attempting to answer clinical questions and determine the best therapy for a particular patient. This article offers a systematic means of categorizing the quality of research reports for clinicians and clinical investigators. A recurring clinical theme of hygiene education is used to exemplify how phrasing the clinical question determines the type of study design that could be used. The article describes the continuum of research reports, and categorizes them by their inherent strengths and weaknesses. The report describes why the research designs in the supreme position of the research hierarchy, are the most valuable to clinicians seeking evidence that defines the best therapy for their patients.

Clinical Trials as Topic↗
PubMed2000

Antioxidant effect of dipyridamole (DIP) and its derivative RA 25 upon lipid peroxidation and hemolysis in red blood cells.

The antioxidant effects of dipyridamol (DIP), a coronary vasodilator, and its derivative RA-25 were compared in intact red blood cells (RBC) and in isolated ghost membranes. Both compounds are quite effective antioxidants in cumene hydroperoxide-induced lipid peroxidation of RBC, showing a much smaller effect for hydrogen peroxide oxidation. The antioxidant effect of DIP was considerably higher than that of RA25. For isolated ghost membranes, the apparent IC50 (the drug concentration that produces 50% inhibition of lipid peroxidation) in cumene hydroperoxide-induced peroxidation was 25 microM, while the maximum protective effect of RA-25 was around 30% in the drug concentration range of 50-100 microM. The drugs can protect the oxidative hemolysis induced by cumene hydroperoxide with a lower effect when the hemolysis is induced by H2O2. The significant antioxidant effect against damages induced by cumene hydroperoxide suggests that DIP, due to its lipophilic character, can interact with RBC membranes, and the protective effect is associated with the binding of the drug to the membrane. On the other hand, RA-25 is more hydrophilic than DIP, binds to the membrane to a smaller extent, and, for this reason, has a lower antioxidant effect.

Animals↗
PubMed1999

Direct evidence for immiscible cholesterol domains in human ocular lens fiber cell plasma membranes.

The molecular structure of human ocular lens fiber cell plasma membranes was examined directly using small angle x-ray diffraction approaches. A distinct biochemical feature of these membranes is their high relative levels of free cholesterol; the mole ratio of cholesterol to phospholipid (C/P) measured in these membranes ranges from 1 to 4. The organization of cholesterol in this membrane system is not well understood, however. In this study, the structure of plasma membrane samples isolated from nuclear (3.3 C/P) and cortical (2.4 C/P) regions of human lenses was evaluated with x-ray diffraction approaches. Meridional diffraction patterns obtained from the oriented membrane samples demonstrated the presence of an immiscible cholesterol domain with a unit cell periodicity of 34.0 A, consistent with a cholesterol monohydrate bilayer. The dimensions of the sterol-rich domains remained constant over a broad range of temperatures (5-20 degrees C) and relative humidity levels (31-97%). In contrast, dimensions of the surrounding sterol-poor phase were significantly affected by experimental conditions. Similar structural features were observed in membranes reconstituted from fiber cell plasma membrane lipid extracts. The results of this study indicate that the lens fiber cell plasma membrane is a complex structure consisting of separate sterol-rich and -poor domains. Maintenance of these separate domains may be required for the normal function of lens fiber cell plasma membrane and may interfere with the cataractogenic aggregation of soluble lens proteins at the membrane surface.

Aged↗
PubMed1999

Distribution and fluidizing action of soluble and aggregated amyloid beta-peptide in rat synaptic plasma membranes.

The effects of soluble and aggregated amyloid beta-peptide (Abeta) on cortical synaptic plasma membrane (SPM) structure were examined using small angle x-ray diffraction and fluorescence spectroscopy approaches. Electron density profiles generated from the x-ray diffraction data demonstrated that soluble and aggregated Abeta1-40 peptides associated with distinct regions of the SPM. The width of the SPM samples, including surface hydration, was 84 A at 10 degrees C. Following addition of soluble Abeta1-40, there was a broad increase in electron density in the SPM hydrocarbon core +/-0-15 A from the membrane center, and a reduction in hydrocarbon core width by 6 A. By contrast, aggregated Abeta1-40 contributed electron density to the phospholipid headgroup/hydrated surface of the SPM +/-24-37 A from the membrane center, concomitant with an increase in molecular volume in the hydrocarbon core. The SPM interactions observed for Abeta1-40 were reproduced in a brain lipid membrane system. In contrast to Abeta1-40, aggregated Abeta1-42 intercalated into the lipid bilayer hydrocarbon core +/-0-12 A from the membrane center. Fluorescence experiments showed that both soluble and aggregated Abeta1-40 significantly increased SPM bulk and protein annular fluidity. Physico-chemical interactions of Abeta with the neuronal membrane may contribute to mechanisms of neurotoxicity, independent of specific receptor binding.

Amyloid beta-Peptides↗
PubMed1999

Quantifying amyloid beta-peptide (Abeta) aggregation using the Congo red-Abeta (CR-abeta) spectrophotometric assay.

Congo red (CR) is a histologic dye that binds to many amyloid proteins because of their extensive beta-sheet structure. The absorbance spectrum of the dye changes upon binding to amyloid. This spectral change has previously been exploited to develop a method to study the interaction of CR with fibrillar beta-sheet insulin fibrils, a model amyloid protein. The amyloid beta-peptide (Abeta) is an amyloid protein which is deposited in the brains of Alzheimer's disease victims. Abeta is toxic to neurons in vitro in a manner that is highly dependent on the assembly of this peptide into beta-sheet fibrils. The CR-insulin assay has been applied as a means of studying the aggregation of Abeta, despite the fact that the CR-insulin procedure was never adequately developed for this purpose. In this study, we modify our original CR-insulin assay specifically for the purpose of quantifying Abeta aggregation and discuss the reasons why application of the CR-insulin method is not valid for this purpose. The CR-Abeta method is equally simple and retains the advantages of speed and lack of necessity for specialized instrumentation or expensive/radioactive reagents. Furthermore, this method can directly provide quantitation of aggregated Abeta in absolute terms (i.e., microg/ml).

Amyloid beta-Peptides↗
PubMed1999

Inhibition of excessive neuronal apoptosis by the calcium antagonist amlodipine and antioxidants in cerebellar granule cells.

Neuronal cell death as a result of apoptosis is associated with cerebrovascular stroke and various neurodegenerative disorders. Pharmacological agents that maintain normal intracellular Ca2+ levels and inhibit cellular oxidative stress may be effective in blocking abnormal neuronal apoptosis. In this study, a spontaneous (also referred to as age-induced) model of apoptosis consisting of rat cerebellar granule cells was used to evaluate the antiapoptotic activities of voltage-sensitive Ca2+ channel blockers and various antioxidants. The results of these experiments demonstrated that the charged, dihydropyridine Ca2+ channel blocker amlodipine had very potent neuroprotective activity in this system, compared with antioxidants and neutral Ca2+ channel blockers (nifedipine and nimodipine). Within its effective pharmacological range (10-100 nM), amlodipine attenuated intracellular neuronal Ca2+ increases elicited by KCl depolarization but did not affect Ca2+ changes triggered by N-methyl-D-aspartate receptor activation. Amlodipine also inhibited free radical-induced damage to lipid constituents of the membrane in a dose-dependent manner, independent of Ca2+ channel modulation. In parallel experiments, spontaneous neuronal apoptosis was inhibited in dose- and time-dependent manners by antioxidants (U-78439G, alpha-tocopherol, and melatonin), nitric oxide synthase inhibitors (N-nitro-L-arginine and N-nitro-D-arginine), and a nitric oxide chelator (hemoglobin) in the micromolar range. These results suggest that spontaneous neuronal apoptosis is associated with excessive Ca2+ influx, leading to further intracellular Ca2+ increases and the generation of reactive oxygen species. Agents such as amlodipine that block voltage-sensitive Ca2+ channels and inhibit cellular oxidative stress may be effective in the treatment of cerebrovascular stroke and neurodegenerative diseases associated with excessive apoptosis.

Amlodipine↗
PubMed1998

The traditional therapeutic paradigm: complete denture therapy.

The art and science of complete dentures for oral restoration has been espoused and debated for over a century. A tradition of clinical mentoring has passed this prosthodontic trust through time to create an educational cycle where the pupil ultimately became the tutor for yet another pupil. Today's clinical techniques and judgments are an amalgamation of these original prosthodontic philosophies. This article will bring forward some procedures for the fabrication of complete dentures for the scrutiny of their scientific bases. Scrutiny does not imply that aspects of therapy not proved in studies of rigorous scientific design are untruths. However, it is incumbent that those aspects of denture therapy regarded as "public domain" by the corpus of the profession be analyzed. It is also incumbent that possible costly or harmful aspects of denture therapy be identified. There is a paucity of "procedural research" in clinical investigations; research that involves performing an invasive or clinician-intensive procedure. This article also discusses the difficulties in performing procedural research as a means of understanding its importance, but also realizing the reasons that this type of research is not prevalent in the dental and health professional literature. The most common types of investigations used to evaluate patient acceptance and function of dentures will also be discussed.

Attitude to Health↗
PubMed1998

Functional results of dental restoration with osseointegrated implants after mandible reconstruction.

We reviewed the cases of 20 cancer patients (mean age 47.4 years) in whom osseointegrated implants were used for dental restoration after mandibular reconstruction between January of 1988 and December of 1994. Seventy-one implants were placed into bone flaps (n = 60) or native mandible (n = 11), an average of 3.55 per patient (range, 2 to 5). Successful integration occurred in 91.5 percent (65 of 71); there were five early failures and one late failure, with no significant difference between the number lost in microvascular flaps (5 of 60) and native mandible (1 of 11) (as determined by Fisher's exact test). Functional evaluation included assessments of diet, speech, and cosmesis. Based on our review, we concluded that (1) implants enhance dental restoration in selected patients, and (2) microvascular bone flaps, including the fibula and iliac crest, are well suited for dental implant restoration.

Adult↗
PubMed1996

Total midface reconstruction after radical tumor resection: a case report and overview of the problem.

We report an unusual repair of a massive midface defect resulting from resection of a recurrent squamous cell carcinoma of the nasal vestibule. The defect included both maxillas, the hard palate, the upper lip, and all nasal and perinasal tissues. After treatment, reconstruction was accomplished using prostheses and autologous tissue transferred from local and distant sites. The osseous component of the transferred tissue permitted placement of osseointegrated implants for fixation of maxillary and nasal prostheses. The rationale for this reconstruction and the problems associated with midface reconstruction after radical tumor resection are discussed.

Carcinoma, Squamous Cell↗
PubMed1995

Partial denture framework design for bone-grafted mandibles restored with osseointegrated implants.

Unilateral osseous reconstruction of a dentate mandible after tumor ablation may be restored with implants and a removable partial denture. Often the remaining dentition is in a "straight line" that does not allow cross-arch stabilization of the framework. Framework design incorporating existing unilateral lingual or buccal retention in the natural dentition and unilateral implant attachments affords a stable, retentive definitive prosthesis for this patient population.

Acrylic Resins↗
PubMed1994

Prescribing nicotine substitutes for tobacco cessation: considerations and contraindications.

This article deals with the topic of nicotine replacement drugs and their use in smoking cessation. Questions frequently arise as to their prescription by dentists. Provided patients are carefully selected on the basis of medical and psychological profiles, there is no ethical or legal contraindication to dentists prescribing these aids. This article reviews the current literature and answers commonly asked questions concerning these effective drugs.

Administration, Cutaneous↗
PubMed1993

Mandible fragment fixation during reconstruction: the splint-and-plate technique.

One of the most popular methods of mandible fragment fixation is the precontoured reconstruction plate technique. Unfortunately, this method is not a reliable option when tumor distorts the mandibular contour or extends through the buccal cortex of the mandible. An alternative to the precontoured reconstruction plate is the splint-and-plate technique of mandible fragment fixation. An application of this appliance and method in 10 patients revealed the technique's advantages. The splint can be applied quickly and does not obstruct the ablative or reconstructive procedure. Further, the splint accurately keys the dentition and reliably maintains temporomandibular joint relationships. Finally, this technique provides a reference point to the exact position of the symphysis and angle when these landmarks have been resected.

Adult↗
PubMed1993

Management of xerostomia in the irradiated patient.

Symptomatic management of xerostomia in the head and neck radiation patient often is a palliative process at best. There are secondary clinical effects, however, that require definitive management. Use of fluorides, antimicrobial rinses, saliva substitutes, and sialagogues is discussed.

Head and Neck Neoplasms↗