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Biomedical subjects

B B Singh

Publications and source records attributed to B B Singh.

At least 73 records · Page 4Linked to original sources
PubMed1994

Diminution of singlet oxygen-induced DNA damage by curcumin and related antioxidants.

Curcumin, the natural antioxidant from turmeric, an Indian spice, and its derivatives have significant abilities to protect plasmid pBR322 DNA against single-strand breaks induced by singlet oxygen (1O2), a reactive oxygen species with potential genotoxic/mutagenic properties. 1O2 was generated at 37 degrees C in an aqueous buffer system by the thermal dissociation of the endoperoxide of 3,3'-(1,4-naphthylene)dipropionate (NDPO2). Among the compounds tested, curcumin was the most effective inhibitor of DNA damage followed by desmethoxycurcumin, bisdesmethoxycurcumin and other derivatives. The observed antioxidant activity was both time- and concentration-dependent. The protective ability of curcumin was higher than that of the well-known biological antioxidants lipoate, alpha-tocopherol and beta-carotene. However, the highest protective ability with saturating concentrations of curcumin did not exceed 50%. The ability of curcumin and its derivatives to protect DNA against 1O2 seems to be related to their structures and may at least partly explain the therapeutic and other beneficial effects of these compounds including anticarcinogenic and antimutagenic properties.

Antimutagenic Agents↗
PubMed1994

High prevalence of thyroid function test abnormalities in chronic schizophrenia.

The thyroid status of 249 patients with chronic schizophrenia (males = 136, females = 113) with a median age of 36 years (range: 16 to 58 years) and a median duration of hospitalisation of 10 years (range: 1 to 30 years) was assessed. Thyroid antibodies (TAb) were found in 51 patients (20%). In female patients, 32 (28%) were TAb positive compared to 13% (n = 152, p = 0.01) in healthy female blood donors. In male patients, the prevalence of TAb was 14% compared to 7% (n = 449, p = 0.01) in healthy male blood donors. Of the 183 patients who had thyroid hormone measurements, 60% had normal test, 5% had elevated TSH and 17% had low TSH. The T4, FT41 and FT31 were significantly lower in those with low or high TSH (p < 0.001) compared to those with normal TSH. Of the 143 patients with normal TSH, 33 (23%) had low T3. In conclusion, there is a spectrum of thyroid function test abnormalities in chronic schizophrenia; this may be related to an abnormality in the central regulation of the hypothalamo-pituitary thyroid axis as well as at the peripheral level. However the association between chronic schizophrenia and the presence of thyroid antibodies, and the clinical relevance of these biochemical abnormalities, are still not clear.

Adolescent↗
PubMed1994

Light microscopic and scanning electron microscopic analyses of dental implants retrieved from humans.

This paper reports analyses obtained from 51 implant cases retrieved from humans and submitted to the AAIDRF-MCG Implant Retrieval Center. The undecalcified samples were embedded in PMMA and examined with scanning electron microscopy and with routine light or Nomarski microscopy. Cases included individual implants as well as 2 mandibles obtained at autopsy. Retrieved implants were sometimes shown to be encapsulated with connective tissue (CT), whereas other implants were apposed by bone, with only minimal CT association. In the latter cases, the implants were apposed by substantial amounts of viable bone. Nomarski microscopy disclosed the orientation and close apposition of the collagen bundles comprising the interfacial bone. In these cases where close bone apposition was observed to the implants, implant fracture was often the cause of failure. Periodontal lesions were reported around some implants showing a marked degree of inflammatory cell infiltrate (ICI). This study underscores the need for evaluation of failed human dental implants. Failure of implants placed longer than 10 years ago (perhaps loaded immediately) may be due to loss of bone support, CT encapsulation, and ICI (i.e., biological failure). Failure of more recently placed implants could also be due to this scenario, but failure was more often ascribed to biomaterial failure.

Alveolar Process↗
PubMed1994

Urban youth, fear of crime, and resulting defensive actions.

One of the most neglected populations studied in victimology has been juveniles. The present study examines the impact of fear of crime among a sample of urban youth on their defensive actions. Studies of urban adult populations have found that a significant number of people fear to venture outside their homes at night. When they do go out, they often take defensive measures to insure their safety. Carrying "mace," whistles, guns, knives, and clubs, for example, is not uncommon. Some have indicated that they have undertaken training in a variety of self-defensive arts and/or keep dogs to protect themselves from the possibility of being victimized. Using data collected from a sample of 1,775 urban youth in 1986 it was found that this population has taken many of the same defensive actions. Only 11% of the sample indicated that they had not taken any defensive actions as a result of fear of crime. Nearly three-fifths took the precaution of having an escort when they went out at night. Learning a technique of self-defense was reported by 19% of the sample; 10% indicated that they carried "mace" or some other type of repellant. Only 4% reported that they carried a whistle because of crime concerns. Significant predictors of personal defensive actions include gender, crime-witnessing status, victimization status and type of victimization (theft vs. witnessing Other defensive actions taken by members of the respondents' households included installing a burglar alarm (22%), keeping a "trained dog" (17%), keeping lights on a night (39%), and installing security locks (38%).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

Analysis of biexponential nuclear magnetic resonance relaxation curves: studies on simulated data.

Application of a Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence to a nuclear spin system consisting of two components, whose spins do not exchange or exchange slowly on the scale of the shorter time constant, results in the nuclear magnetization Mz of the spin system decaying according to the relation Mz = Ma exp(-t/Ta)+Mb exp(-t/Tb)+K+E where Ma,Ta are the intensity and transverse relaxation time of one component, Mb and Tb are the corresponding values for the second component, K is a constant and E is the contribution due to noise. Data simulation according to the above function was carried out with different values for the parameters Ma, Ta, Mb, Tb and K, the noise component being normally distributed with mean zero. For each set of parameters, the data generation was repeated a number of times with a different noise content and in each case, the parameters were estimated using a non-linear least square curve fitting procedure. The mean and percent coefficient of variation (CV) of each parameter was calculated. The value of CV is taken as a measure of the uncertainty in the estimated value of the parameter. It is found that the uncertainty in the estimated values of the parameters is due to the random noise. The range of data points is more critical than the number of data points used in curve fitting. Moreover, the uncertainty associated with each parameter increases with decreasing Ma/Mb ratio and increases with increasing Ta/Tb ratio. Higher signal to noise ratios will be required to analyse data with low Ma/Mb and high Ta/Tb ratios.(ABSTRACT TRUNCATED AT 250 WORDS)

Computer Simulation↗
PubMed1993

Influence of palm oil or its tocotrienol-rich fraction on the lipid peroxidation potential of rat liver mitochondria and microsomes.

The effect of palm oil, a widely used vegetable oil, rich in tocotrienols, on peroxidation potential of rat liver was examined. Long-term feeding of rats with palm oil as one of the dietary components significantly reduced the peroxidation potential of hepatic mitochondria and microsomes. As compared to hepatic mitochondria isolated from rats fed control or corn oil-rich diet, those from palm oil-fed group showed significantly less susceptibility to peroxidation induced by ascorbate and NADPH. However, in microsomes, only NADPH-induced lipid peroxidation was significantly reduced in rats fed palm oil rich-diet. Though the accumulation of thiobarbituric acid reactive substances during ascorbate-induced lipid peroxidation in mitochondria from rats fed corn oil-rich diet supplemented with tocotrienol-rich fraction (TRF) of palm oil was similar to that of control rats, the initial rate of peroxidation was much slower than those from control or corn oil fed diets. Our in vitro studies as well as analyses of co-factors related to peroxidation potential indicated that the observed decrease in palm oil-fed rats may be due to increased amount of antioxidants in terms of tocotrienol as well as decrease in the availability of substrates for peroxidation.

Animals↗
PubMed1992

Chemical radiosensitizers in cancer therapy.

The development of effective low-LET radiation therapy for cancer has been hindered by the lack of consistent differential responses to radiation between tumor and normal tissues. One major difference between many solid tumors and the surrounding normal stroma is the presence of hypoxic foci in solid tumors due to the inadequate supply of nutritional needs as a result of the breakdown of microvasculature. Consequently, failure of conventional radiotherapy and local recurrences are in part attributed to the radioresistant hypoxic cell populations, present in the tumor. Local cure/control rates of a tumor can be increased only by an effective increase in the radiation dose. At the same time, an increase in such a dose would damage the oxic normal stroma, more than the hypoxic tumor cells. Hence, specific modification of tumor radiosensitivity by the use of chemical radiosensitizers, in combination with conventional radiotherapy, is an attractive alternative. Many clinicians and radiotherapists are skeptical about the outcome of using radiosensitizers in patients. Nevertheless, a vast amount of information is currently available regarding the first- and second-generation radiosensitizers both in murine and in human tumors. As a result, it is hoped that eventually a radiosensitizing drug would be discovered/synthesized that will overcome the drawbacks so far encountered in their use in the clinic. In this article, the development of chemical radiosensitizers since the early sixties, the basis for their selection, their mechanism(s) of action, and the results obtained with the various groups of radiosensitizers are reviewed.

Animals↗
PubMed1991

Felodipine in combination with a beta-adrenoceptor blocker as an effective substitute for triple therapy in severe hypertension. The Australian Felodipine Multicentre Study Group.

We have studied the efficacy and tolerability of felodipine plus a beta-adrenoceptor blocker in 79 patients with essential hypertension previously treated with a combination of three or more anti-hypertensive agents, one of which was a beta-adrenoceptor blocker. After a 4-week run-in period on the same beta-blocker plus placebo (as a substitute for the other agents in the regimen), felodipine was added and its dose titrated to achieve a supine diastolic blood pressure or less than 90 mm Hg. This was followed by a 12-week maintenance phase in all patients, and 47 patients entered an optional long-term follow-up for an additional 9 months. The mean supine blood pressure was 149/88 mm Hg at entry and 174/108 mm Hg after the run-in phase. Felodipine significantly reduced the blood pressure to 142/85 mm Hg after dose titration and to 141/84 mm Hg after 12 weeks, 94% of patients achieving a supine diastolic blood pressure of 90 mm Hg or below. This reduction was maintained in the patients who were followed for 12 months. The adverse events recorded were usually mild, transient, and typical for an effective precapillary vasodilator. Nine of 74 patients (11%) were withdrawn in the first phase of the study because of adverse events and 5 of 47 patients were withdrawn during the long-term follow-up. These results show that the efficacy and tolerability of a combination of felodipine with a beta-blocker allow a simplified regimen for hypertensive patients who were previously taking three or more drugs for satisfactory blood pressure control.

Adolescent↗
PubMed1990

Binding and uptake of N-nitrosonornicotine by oral epithelial cells.

N-nitrosonornicotine (NNN), a significant nitrosamine component of tobacco binds to and is taken up by cells prior to its activation by intracellular enzymes. A variety of factors may affect the binding of substances to a cell including the cell type, medium composition and the cell membrane lipid composition. This study examines the binding and uptake of NNN to various cell types and relates these to the cells' lipid composition. Hamster buccal pouch keratinocytes were exposed to NNN and the amount of bound NNN determined. This was compared with cells pretreated with 12-0-tetradecanoylphorbol-13-acetate (TPA). While the keratinocytes bound significant amounts of NNN, this binding was not specific. Pretreatment of the cells with TPA significantly increased the amount of NNN bound. Cultures of human gingival fibroblasts and a human liver cell line also bound NNN, in quantities greater than that bound to the keratinocytes. The TPA caused changes in long chain unsaturated fatty acids although major changes in lipid metabolism were not detected. The fatty acid composition of the liver cells more closely resembled that of the TPA treated keratinocytes than the untreated ones. The data suggest that NNN binds to the cells non-specifically and the binding may be related to the amount of long-chain, unsaturated fatty acids present.

Animals↗
PubMed1990

Ultrastructural investigations of the bone and fibrous connective tissue interface with endosteal dental implants.

The interface between the tissues of the oral cavity and ceramic and titanium cylindrical endosteal dental implants was investigated with correlated light microscopy, transmission electron microscopy and scanning electron microscopy. This study suggested that mandibular bone can directly interface and form an intimate association with one-stage endosteal dental implants. This potential attachment matrix is composed of a composite of calcified bone, and an osteoid unmineralized matrix in association with an apparent osteogenic connective tissue. Further, results from this study suggested that at a level inferior to the junctional epithelium, and superior to the level of crestal bone, fibrous connective tissue can attach to the dental implant. This non-loadbearing attachment of gingival connective tissue could, by contact inhibition, prevent apical epithelial migration. In association with previously documented epithelial attachment, such apical support and connective tissue attachment appears to suggest that endosteal dental implants can be adequately maintained in the oral cavity.

Animals↗
PubMed1989

Studies on indomethacin as a potentiator for hyperthermic and radiation responses in a mouse fibrosarcoma.

Indomethacin, a non-steroidal anti-inflammatory drug which is also a calcium antagonist and an inhibitor of prostaglandin synthesis was observed to have a chemotherapeutic effect in a mouse fibrosarcoma. More significantly, administration of the drug before exposure to either radiation or hyperthermia, enhanced their effects. Apart from tumor growth delay, tumor cures were also observed in all the three modalities tested. The data suggests a potential anti-cancer role for indomethacin in combination modalities.

Animals↗
PubMed1989

Effect of early human malnutrition on waking and sleep organization.

In order to evaluate the effect of early human malnutrition (EHM) on waking and sleep organization, a group of 12 infants malnourished (M) from birth were investigated in their first year of life through 24-h polygraphic recordings. The same infants were recorded again after nutritional rehabilitation (R). A group of 12 age-paired normal infants served as controls (C). Both young (less than 4 months) and older (greater than or equal to 4 months) M infants showed a distribution of classes of waking duration different from that of C while the trend with age of the longest sustained waking (LSW) is similar in M and in C infants. The durations distribution of sleep episodes does not differ between M and C infants, while the longest sustained sleep (LSS) is significantly shorter in M than in C infants. The LSW is less clearly located in the day-time and the LSS is less clearly located in the night-time in M infants as compared to C infants. The quiet sleep-paradoxical sleep cycles are significantly shorter in older M infants because of the reduction of quiet sleep. Nutritional rehabilitation tends to improve waking and sleep organization.

Child, Preschool↗
PubMed1989

Relationship between respiratory pauses and heart rate during sleep in normal premature and full-term newborns.

To investigate the relationship between central respiratory pauses and heart rate, we performed polygraphic recordings in 23 normal newborns (35 to 41 weeks conceptional age). We monitored the electroencephalogram, rapid eye movements, movements of the upper and lower limbs, chin and diaphragmatic electromyogram, electrocardiogram, thoracic and abdominal respiratory movements, air flow and transcutaneous PO2. Heart rate changes were analysed by computer measurement of R-R intervals and by cardiotachography. Respiratory pauses occurring after body movements and those not preceded by movements were studied separately. We analysed 1128 respiratory pauses greater than 3 s duration. No respiratory pause lasted more than 12 s. Independently of age, sleep state and respiratory pause duration, heart rate was significantly lower at the onset of respiratory pause, compared to control periods (selected away from the pause: 10 s before its onset and 20 s after its end). Heart rate slowed still further through the respiratory pause and reverted toward the baseline level after its end. When no movements preceded the respiratory pause, heart rate just before the pause was lower compared to control periods. These findings suggest the existence of simultaneous central commands responsible for both respiratory pause and heart rate deceleration.

Electrophysiology↗
PubMed1988

In vivo effects of Sn-1,2-dioctanoylglycerol, TPA and A23187 on hamster cheek pouch epithelium.

Cheek pouches of male Syrian golden hamsters were topically treated with a single dose of TPA (.5 microgram), calcium ionophore A23187 (75 micrograms) or Sn-1,2-dioctanoylglycerol (DiC8) (500 micrograms) dissolved in 0.25 ml acetone. Acetone-treated animals served as controls. After 48 h the mitotic index for the control group was 1.1 +/- 0.1 per 1 mm of the basement membrane length. All the test congeners exhibited higher mitotic indices than controls: TPA (4.8 +/- 0.4), A23187 (3.9 +/- 0.3), DiC8 (2.1 +/- 0.2). All groups exhibited an increase in the epithelial thickness manifested by cellular hyperplasia. The treatment of the pouches with the anti-inflammatory agent fluocinolone acetonide inhibited the mitogenic and hyperplasiogenic affects on the epithelium induced by the various test chemicals. These studies indicate a possible role of calcium-phospholipid dependent protein kinase (protein kinase C) in the mediation of oral epithelial cell proliferation.

Animals↗
PubMed1988

The scientific basis for dental implant therapy.

Dental and oral implantology have rapidly moved into the mainstream of dentistry in the last ten years with a phenomenal growth based on rapidly expanding technology, increasing public interest, and the reporting of sound scientific data. This paper reviews current knowledge about implant tissue reactions and identifies areas where additional scientific inquiry is needed. Bone- and soft-tissue healing around dental implants varies greatly depending upon the form of the implant, biomaterial used, and surgical approach. Controversy exists as to whether a direct bony-biomaterial interface is preferable over a bone-connective tissue-biomaterial interface. Scientific data are required to document whether intervening molecular layers of glycoproteins exist between implant and bone, and what role is played by these structures relative to the implant-bone interface. The adaptation of regenerated gingival epithelium to an implant is critical for the development of a perimucosal seal. Many scientific questions remain unanswered about this seal and its role in maintenance of implant longevity. Controlled clinical trials must be carried out to determine clinical serviceability standards for patients. Resolving these areas of concern and understanding the biological reactions involved will require in-depth scientific inquiry by clinician and scientist alike to make dental implantology a highly acceptable and predictable treatment modality. Even with these controversies and lack of comprehensive comparison studies, dental implantology is an exciting treatment concept that makes considerable demands upon the surgical, prosthetic, periodontal, and restorative skills of today's practitioners, and on their scientific understanding as well.

Biocompatible Materials↗