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Biomedical subjects

M C Lynch

Publications and source records attributed to M C Lynch.

At least 19 recordsLinked to original sources
PubMed2004

Adjunctive benefit of an essential oil-containing mouthrinse in reducing plaque and gingivitis in patients who brush and floss regularly: a six-month study.

BACKGROUND: Mechanical methods of oral hygiene can be complemented by the use of chemotherapeutic mouthrinses. The authors sought to quantify the additional benefit provided by an essential oil-, or EO-, containing mouthrinse in reducing plaque and gingivitis in patients who brush and floss regularly. METHODS: The authors randomly assigned patients with gingivitis to one of three treatment groups: brushing and rinsing with a control mouthrinse, or BC; brushing, flossing and rinsing with a control mouthrinse, or BFC; or brushing, flossing and rinsing with an EO-containing mouthrinse, or BFEO. Patients received a dental prophylaxis at baseline, and the authors followed them for six months. RESULTS: Of 246 enrolled subjects enrolled in the study, 237 subjects were evaluable at the study's conclusion. After six months, the subjects using the BFEO regimen had statistically and clinically significant lower mean Modified Gingival Index, or MGI, scores and Plaque Index, or PI, scores than did subjects in the BC group (29.9 percent and 56.3 percent, respectively; P < .001). Subjects in the BFC group had statistically significantly lower mean MGI and PI scores than did subjects in the BC group (11.2 percent and 9.3 percent, respectively; P < .001). Subjects in the BFEO group exhibited statistically and clinically significantly lower mean scores for MGI and PI than did subjects in the BFC group (21 percent and 51.9 percent, respectively; P < .001). CONCLUSIONS: This study confirms that for patients with gingivitis who brush and floss routinely, the adjunctive use of an EO-containing mouthrinse provides a clinically significant and meaningful additional benefit in reducing plaque and gingivitis. CLINICAL IMPLICATIONS: An EO-containing mouthrinse is an effective adjunct to regular brushing and flossing. Therefore, the BFEO regimen can be beneficial for patients with gingival inflammation.

Adolescent↗
PubMed2001

Progression of active trachoma to scarring in a cohort of Tanzanian children.

Risk factors for the incidence of scarring are needed to inform trachoma control programs in countries hyperendemic for this blinding disease. A cohort of pre-school children with constant, severe trachoma, and an age, sex, and neighborhood matched cohort of children without constant severe trachoma were followed for seven years to determine the incidence of scarring. The incidence of scarring in the children with constant severe trachoma was 29.2% versus 9.6% in the comparison group. In a model adjusting for multiple factors, significant predictors of scarring were increasing age, female, and constant severe trachoma (OR = 4.85, 95% CL = 2.05, 11.40). Infection with C. trachomatis at follow up was also associated with scarring in both groups of children. It is likely that these children have a different host response to infection, and represent a subgroup at high risk for the blinding complications of trachoma. Reducing exposure to infection in the community through antibiotics and changes in hygiene practices is still the most promising control strategy.

Child↗
PubMed2000

Reactive oxidizing species produced near the plasma membrane induce apoptosis in bovine aorta endothelial cells.

Many cytotoxic agents initiate apoptosis by generating reactive oxidizing species (ROS). The goal of this study was to determine whether apoptosis could be induced by initial reactions of ROS near the plasma membrane. Bovine aorta endothelial cells (BAEC) were illuminated with evanescent wave visible radiation, which has limited penetration into the basal surface of cells, or by trans-radiation. Imaging of fluorescent dyes localizing in the plasma membrane, mitochondria, or nucleus confirmed that evanescent wave radiation excited only dyes in and near the plasma membrane. Singlet oxygen, an ROS generated by photosensitization, has a very short lifetime, ensuring that it oxidizes molecules residing in or very close to the plasma membrane when evanescent wave radiation is used. Cells with condensed nuclei were considered apoptotic and were quantified after treatment with varying doses of light. Annexin V staining without propidium iodide staining confirmed that these cells were apoptotic. The doses required to induce apoptosis using evanescent wave radiation were 10-fold greater than those needed for trans-irradiation. Quantitative analysis of the evanescent wave penetration into cells supports a mechanism in which the singlet oxygen created near the plasma membrane, rather than at intracellular sites, was responsible for initiation of apoptosis.

Animals↗
PubMed2000

Singlet oxygen, but not oxidizing radicals, induces apoptosis in HL-60 cells.

Oxidizing species (OS), produced by photosensitization or derived from cytotoxic agents, activate apoptotic pathways. We investigated whether two different OS, formed at the same subcellular sites, have equivalent ability to initiate apoptosis in HL-60 cells. Our previous work showed that absorption of visible light by rose bengal (RB) produces singlet oxygen exclusively, whereas absorption of ultraviolet A produces RB-derived radicals in addition to singlet oxygen. Singlet oxygen, but not the RB-derived radicals, induced nuclear condensation and DNA fragmentation into nucleosome-size fragments in a dose dependent manner. In contrast, the RB-derived radicals caused greater lipid oxidation than singlet oxygen. These results indicate that different OS, produced at the same subcellular sites, do not have the same ability to induce apoptosis and that the ability of an OS to initiate lipid oxidation does not necessarily correlate with its ability to induce apoptosis.

Apoptosis↗
PubMed1999

Caspase-8 mediates caspase-3 activation and cytochrome c release during singlet oxygen-induced apoptosis of HL-60 cells.

We reported previously that singlet oxygen, generated by irradiation of rose bengal with visible light, induced apoptosis in human promyelocytic leukemia HL-60 cells. However, the mechanism of apoptosis caused by this reactive oxygen species is unclear. In this study, we demonstrate that singlet oxygen induced caspase-3 activation and Z-DEVD-FMK, a caspase-3 inhibitor, blocked apoptosis induction, while caspase-1 activity was not detectable and the caspase-1 inhibitor Z-YVAD-FMK had a very limited effect on apoptosis. This suggests that the activation of caspase-3 by singlet oxygen is essential for the commitment of cells to undergo apoptosis. Further studies showed that singlet oxygen induced an increase in caspase-8 activity and a reduction in mitochondrial cytochrome c. Time course analysis indicated that the cleavage of caspase-8 precedes that of caspase-3. In addition, blockade of caspase-8 by Z-IETD-FMK inhibited cleavage of pro-caspase-3 and prevented loss of mitochondrial cytochrome c. These results suggest that caspase-8 mediates caspase-3 activation and cytochrome c release during singlet oxygen-induced apoptosis in HL-60 cells.

Apoptosis↗
PubMed1999

Role of superoxide dismutase activity in the physiology of Porphyromonas gingivalis.

Porphyromonas gingivalis is a gram-negative, obligate anaerobe strongly associated with chronic adult periodontitis. A previous study has demonstrated that this organism requires superoxide dismutase (SOD) for its modest aerotolerance. In this study, we have constructed a mutant deficient in SOD activity by insertional inactivation as well as a sod::lacZ reporter translational fusion construct to study the regulation of expression of this gene. We have confirmed that SOD is essential for tolerance to atmospheric oxygen but does not appear to be protective against hydrogen peroxide or exogenously generated reactive oxygen species. Furthermore, the sod mutant appeared to be no more sensitive to killing by neutrophils than the parental strain 381. SOD appears to be protective against oxygen-dependent DNA damage as measured by increased mutation to rifampin resistance by the sod mutant. Use of the sod::lacZ construct confirmed that SOD expression is maximal at mid-log phase and is influenced by oxygen, temperature, and pH. However, expression does not appear to be significantly affected by iron depletion, osmolarity, or nutrient depletion. The transcription start site of the sod gene was determined to be 315 bp upstream of the sod start codon and to be within an upstream open reading frame. Our studies demonstrate the essential role that SOD plays in aerotolerance of this organism as well as the selective induction of this enzyme by environmental stimuli.

Adult↗
PubMed1998

Activation of protein kinase C is required for protection of cells against apoptosis induced by singlet oxygen.

We evaluated the role of protein kinase C (PKC) in the regulation of apoptosis triggered by singlet oxygen. Activation of PKC by short-term 12-O-tetradecanoyl phorbol 13-acetate (TPA) treatment inhibited apoptosis, whereas inhibition of PKC with several inhibitors potentiated this process. The antiapoptotic effect of TPA was accompanied by phosphorylation of extracelluar signal-regulated kinase 1/2 (ERK1/2). Pretreatment of cells with MEK inhibitor, PD98059, inhibited TPA-induced phosphorylation of ERK1/2 and the cytoprotective ability of TPA. These results suggest that activation of PKC in HL-60 cells confers protection against apoptosis induced by singlet oxygen and that ERK1/2 mediates antiapoptotic signaling of PKC.

Apoptosis↗
PubMed1998

Benzoyl peroxide increases UVA-induced plasma membrane damage and lipid oxidation in murine leukemia L1210 cells.

Ultraviolet A radiation induces oxidative stress and cell damage. The purpose of this investigation was to examine whether ultraviolet A-induced cell injury was amplified by the presence of a non-ultraviolet A absorbing molecule capable of generating free radicals. Benzoyl peroxide was used as a lipid soluble potential radical-generating agent. Plasma membrane permeability assessed by trypan blue uptake was used to measure cell damage in murine leukemia L1210 cells. Cells were irradiated with a pulsed Nd/YAG laser at 355 nm using 0-160 J per cm2. The ratio of the fluence-response slope in the presence of 40 microM benzoyl peroxide to that of irradiated controls was 4.3 +/- 2.6. Benzoyl peroxide alone or benzoyl peroxide added after irradiation did not cause increased trypan blue uptake. The ratio of the fluence-response slopes in the presence of 40 microM benzoyl peroxide to that of irradiated controls was 4.7 +/- 1.4 when cells were irradiated (0-43 J per cm2) with a xenon lamp, filtered to remove wavelengths <320 nm. The increased trypan blue uptake in 355 nm-irradiated cells in the presence of benzoyl peroxide was inhibited in a concentration-dependent manner by butylated hydroxytoluene, vitamin E, and trolox, a water-soluble vitamin E derivative. Lipid oxidation, assessed as thiobarbituric acid reactive substances, was significantly increased in samples irradiated with ultraviolet A in the presence of benzoyl peroxide at fluences >34 J per cm2. The increased trypan blue uptake and thiobarbituric acid reactive substances were inhibited by butylated hydroxytoluene. These results suggest that agents not absorbing ultraviolet A radiation may enhance ultraviolet A-initiated oxidative stress in cells.

Absorption↗
PubMed1998

Risks of occupational exposure to latex gloves.

The extraordinary increase in latex glove use in dentistry within the past decade has created a potential occupational hazard in the form of adverse reactions to components found in these gloves. Reactions may range from dry, itchy skin to a life-threatening, anaphylactic response. Management of these conditions may be as simple as switching glove brands; but in the most severe cases, it may entail the need to create a latex-free environment for the safety of the affected health care worker. This article reviews the pathophysiology, epidemiology, diagnosis and management of these conditions and provides references for more in-depth reading on the subject.

Anaphylaxis↗
PubMed1997

Social and cultural factors affecting rates of regular retreatment of mosquito nets with insecticide in Bagamoyo District, Tanzania.

Insecticide-treated mosquito nets have an impact on mortality and morbidity in young children under controlled conditions. When integrated into larger control programs, there is the danger that rates of regular retreatment of the nets with insecticide will drop, greatly limiting their effectiveness as a public health intervention. In Bagamoyo District, Tanzania, rates of retreatment dropped significantly when payment for the insecticide was introduced. A series of neighbourhood (hamlet) meetings were held in all study villages to discuss people's concerns about the insecticide and ways to increase rates of retreatment. Although changes were made in the procedure for retreatment, rates of retreatment remained lower than expected and showed marked variation within as well as between villages. We then conducted unstructured key informant interviews as well as informal discussions in a village with strong variation between different sectors of the villages in rates of retreatment. While logistical problems were most frequently cited as reasons not to bring nets for retreatment, political and social divisions within the community provided a better explanation. This is borne out by the low response to rearrangements in logistics which made retreating the nets significantly easier for households, and the higher response when changes were made in the channels of communication as well as the logistic features. It is clearly more difficult for villagers to appreciate the benefits of the insecticide than those of the nets. Great emphasis needs to be placed on the insecticide and its beneficial effects from the outset for any large-scale programme to be sustainable.

Bedding and Linens↗
PubMed1996

Comparison of photosensitized plasma membrane damage caused by singlet oxygen and free radicals.

The efficiency and selectivity of photosensitized damage to membrane functions may be influenced strongly by the identity of the initial reactive species formed by the photosensitizer. To test this possibility, a photosensitizer, rose bengal (RB), was used that resides in the plasma membrane and which generates singlet molecular oxygen (1O2*) upon excitation with visible light, and radicals plus 1O2* upon excitation with UV radiation. With this approach, 1O2* and radicals are formed at the same locations in the plasma membrane. The response of three plasma membrane functions, namely, proline transport, membrane potential, and membrane impermeability to charged dye molecules, was assessed. The efficiencies of the responses in the presence and absence of oxygen were compared per photon absorbed by RB at two wavelengths, 355 nm (UV excitation) and 532 nm (visible excitation). The efficiency of oxygen removal before irradiation was assessed by measuring the RB triplet lifetime. The three membrane functions were inhibited more efficiently at 355 nm than at 532 nm in the presence of oxygen indicating that the radicals are more effective at initiating damage to membrane components than 1O2*. The ratio of photosensitized effects at the two wavelengths in the presence of oxygen was the same for two membrane functions but not for the third suggesting that 1O2* and radicals initiate a common mechanistic pathway for damage to some membrane functions but not to others. Removing oxygen reduced the efficiency of 355 nm-induced photosensitization by factors of 1.4 to 7. The sensitivity of the three membrane functions to 1O2*-initiated damage varied over a factor of 50 whereas radical initiated damage only varied by a factor of 15. In summary, these results indicate that radicals and 1O2* formed at the same locations in the plasma membrane vary in their efficiency and specificity for membrane damage but may, in some cases, operate by a common secondary damage mechanism in the presence of oxygen.

Animals↗
PubMed1996

Intensity-dependent enzyme photosensitization using 532 nm nanosecond laser pulses.

The intensity dependence of the rose bengal (RB)-photosensitized inhibition of red blood cell acetylcholinesterase has been studied experimentally and the results compared to a quantitative excitation/deactivation model of RB photochemistry. Red blood cell membrane suspensions containing 5 microM RB were irradiated with 532 nm, 8 ns laser pulses with energies between 1 and 98.5 mJ. A constant dose (7 J) was delivered to all samples by varying the total number of pulses. At incident energies greater than approximately 4.5 mJ/pulse, the efficiency for photosensitized enzyme inhibition decreased as the energy/pulse increased. The generation of RB triplet state was monitored as a function of laser energy and the triplet-triplet absorption coefficient was determined to be 1.9 x 10(4) M-1 cm-1 at 530 nm. The number of singlet oxygen molecules produced at each intensity was calculated from both the physico-mathematical model and from laser flash photolysis results. The results indicated that the photosensitized inhibition of acetylcholinesterase was exclusively mediated by singlet oxygen, even at the highest laser intensities employed.

Chemical Phenomena↗
PubMed1994

An efficient oxygen independent two-photon photosensitization mechanism.

A novel oxygen-independent photosensitization mechanism from the upper triplet state (Tn) of rose bengal has been demonstrated by selectively populating Tn by sequential two-color laser excitation. Products formed from Tn inhibit red blood cell acetylcholinesterase and decrease viability of P388D1 mouse macrophage monocyte cells as measured by trypan blue exclusion assay. Laser flash photolysis studies indicate that Tn reacts efficiently, as evidenced by permanent photobleaching of T1 absorption, with chemical yields approaching unit efficiency. This mechanism may have application for oxygen deficient photosensitization under high intensity, pulsed laser irradiation.

Acetylcholinesterase↗
PubMed1990

A new radiological method for assessing long bone growth in the small laboratory animal.

The growth of the immature rat tibia has been measured following five different growth stimulating procedures. These comprised proximal periosteal release, proximal periosteal release with insertion of dissimilar metal wire, repeated proximal periosteal release, distal periosteal release and full periosteal stripping of the diaphysis. The new radiographic method of measurement employed, utilizes a photographic technique. A reproducible measurement of the rate of long bone growth in the small experimental animal is possible.

Animals↗