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Biomedical subjects

H Mohan

Publications and source records attributed to H Mohan.

At least 37 records · Page 2Linked to original sources
PubMed2000

Oxidative degradation of triazine derivatives in aqueous medium: a radiation and photochemical study.

Pulse and steady state radiolysis techniques have been used to determine the bimolecular rate constants and to investigate the spectral nature of the intermediates and the degradation induced by hydroxyl radicals ((*)OH) with 1,3,5-triazine (T), 2,4, 6-trimethoxy-1,3,5-triazine (TMT), and 2,4-dioxohexahydro-1,3, 5-triazine (DHT) in aqueous medium. A competitive kinetic method with KSCN as the (*)OH scavenger was used to determine the rate constants for the reaction of (*)OH with T, TMT, and DHT. The bimolecular rate constants are 3.4 x 10(9), 2.06 x 10(8), and 1.61 x 10(9) dm(3) mol(-)(1) s(-)(1) respectively, for T, TMT, and DHT at pH approximately 6. The transient absorption spectra obtained from the reaction of (*)OH with T, TMT, and DHT have single absorption maxima at 320, 300, and 300 nm, respectively, and were found to undergo a second-order decay. The formation of TOH(*) [C(6)OH-N(5)-yl radical], TMTOH(*) [N(5)OH-C(6)-yl radical], and DHT(*) [C(6)-yl radical] is proposed from the initial attack of (*)OH with T, TMT, and DHT, respectively. A complete degradation of TMT (10(-3) mol dm(-3)) was obtained after absorbed doses of 5 kGy in N(2)O-saturated solutions and 16 kGy in aerated solutions. A similar degradation pattern was obtained with DHT in N(2)O-saturated solutions. Complete degradation was observed with an absorbed dose of 7 kGy. On the basis of the results from both pulse and steady state radiolysis, a possible reaction mechanism involving (*)OH-mediated oxidative degradation is proposed. A complete photodecomposition of DHT was also observed in the presence of ferric perchlorate using ultraviolet light at low pH. Photoinduced electron transfer between Fe(III) and DHT in the Fe(III)-DHT complex and subsequent formation of DHT(*) are proposed to be the major processes that lead to the complete degradation of DHT at pH 3.

Gamma Rays↗
PubMed2000

Suprasellar malignant mixed germ cell tumour presenting as craniopharyngioma.

A 15 year old boy presented with diminution in vision of both eyes, diabetes insipidus and hypopituitarism. MRI was suggestive of a large suprasellar and retrosellar craniopharyngioma with stretching of the optic chiasma. Histopathological findings on the first surgical specimen were interpreted as a craniopharyngioma. He was reoperated on account of clinical deterioration and increase in tumour size. Histological examination this time revealed derivatives of all three germ cell lineages along with areas of embryonal carcinoma, and yolk sac tumour besides squamous cysts, establishing the diagnosis of malignant mixed germ cell tumour. Serum and CSF were strongly positive for alpha foetoproteins.

Adolescent↗
PubMed1999

Dermatofibrosarcoma protuberans metastasizing to lymph nodes: a case report and review of literature.

Dermatofibrosarcoma Protuberans (DFSP) is an uncommon cutaneous soft tissue tumor. It is locally invasive and is known to recur. Metastases are rare and occur most commonly to the lungs. Metastasis to lymph nodes is extremely rare with only a few case reports in literature. The management strategy for such lymph node metastases remains controversial because of rarity of the condition. We report a case of DFSP of the lower limb with definite inguinal node secondaries managed by loco-regional surgery. We recommend that block dissection of lymph nodes should be performed in all cases with secondaries. J. Surg. Oncol. 1999;72;178-180.

Adult↗
PubMed1999

Parathyroid cyst: a rare cause of an anterior neck mass.

Parathyroid cysts are rare. Most of them present in the anterior neck as cystic neck swellings. A case of cervical parathyroid cyst is presented, along with a brief review of the literature regarding the aetiology, clinical features, diagnosis and management of this condition.

Adult↗
PubMed1998

Oxidative damage induced by the fullerene C60 on photosensitization in rat liver microsomes.

We have examined the ability of a commonly used fullerene, C60, to induce oxidative damage on photosensitization using rat liver microsomes as model membranes. When C60 was incorporated into rat liver microsomes in the form of its cyclodextrin complex and exposed to UV or visible light, it induced significant oxidative damage in terms of (1) lipid peroxidation as assayed by thiobarbituric acid reactive substances (TBARS), lipid hydroperoxides and conjugated dienes, and (2) damage to proteins as assessed by protein carbonyls and loss of the membrane-bound enzymes. The oxidative damage induced was both time- and concentration-dependent. C60 plus light-induced lipid peroxidation was significantly inhibited by the quenchers of singlet oxygen ((1)O2), beta-carotene and sodium azide, and deuteration of the buffer-enhanced peroxidation. These observations indicate that C60 is an efficient inducer of peroxidation and is predominantly due to (1)O2. Biological antioxidants such as glutathione, ascorbic acid and alpha-tocopherol significantly differ in their ability to inhibit peroxidation induced by C60. Our studies, hence, indicate that C60, on photosensitization, can induce significant lipid peroxidation and other forms of oxidative damage in biological membranes and that this phenomenon can be greatly modulated by endogenous antioxidants and scavengers of reactive oxygen species.

Animals↗
PubMed1998

Tuberculosis of the pyriform fossa--a rare entity.

Tuberculosis of the pharynx is less common than tuberculosis of the larynx. We present a rare case of tuberculosis of the pyriform fossa which clinically masqueraded as a malignancy. Our patient showed a prompt improvement in symptoms after commencing antitubercular treatment.

Adult↗
PubMed1997

Inter-relationship of zinc levels in serum and semen in oligospermic infertile patients and fertile males.

Infertility is a problem affecting 10-12% of couples. Zinc is necessary for growth, sexual maturation and reproduction. Semen analysis is helpful in ascertaining the evidence of spermatogenesis, sperm transport, sperm quantity and quality and also provides clue to the functioning of the accessory glands i.e. seminal vesicles and prostate. The present study was conducted in 50 oligospermic infertile males and control group consisting of 25 normospermic known fertile males. Semen and Serum samples were obtained from each case in study as well as control group. Semen and serum were processed by wet ash method. The seminal and serum zinc levels of each case in study and control group were estimated. Statistically, serum zinc and semen zinc levels were significantly lower in infertile patients than fertile males. A significant correlation was observed between serum and semen zinc levels in study group.

Adult↗
PubMed1996

Caffeine as an antioxidant: inhibition of lipid peroxidation induced by reactive oxygen species.

Caffeine (1,3,7-trimethyl xanthine), an ingredient of coffee, has been investigated for its potential antioxidant activity against oxidative damage to rat liver microsomes. Such damage was induced by three reactive oxygen species of cardinal importance in causing membrane damage in vivo namely hydroxyl radical (.OH), peroxyl radical (ROO.) and singlet oxygen (1O2). The results obtained showed that caffeine was an effective inhibitor of lipid peroxidation, at millimolar concentrations, against all the three reactive species. The extent of inhibition was high against peroxidation induced by .OH, medium against 1O2 and low against ROO. In general, the antioxidant ability of caffeine was similar to that of the established biological antioxidant glutathione and significantly higher than ascorbic acid. Investigations into the possible mechanisms involved in the observed antioxidant effect reveal that the quenching of these reactive species by caffeine may be one of the possible factor responsible. The rate constant of caffeine with .OH was 7.3 x 10(9) M-1 s-1 and with 1O2 it was 2.9 x 10(7) M-1 s-1. Considering their potential for damage, half-life estimates and generation in biological systems, the ability of caffeine to inhibit oxidative damage induced by these reactive species in membranes suggest one more positive attribute of caffeine, whose daily intake as coffee may be considerable in most populations.

Animals↗
PubMed1996

Mechanisms of protection by buthionine sulphoximine against gamma-ray-induced micronuclei in polychromatic erythrocytes of mouse bone marrow.

The effect of pretreatment with buthionine sulphoximine (BSO) on the radiosensitivity of mouse bone marrow cells was studied using the in vivo micronucleus test. Varying concentrations of BSO were injected into mice by intraperitoneal injection 2 h before irradiation, and the frequency of micronuclei in polychromatic erythrocytes (MnPCEs) of bone marrow were scored. Treatment with BSO resulted in a significant reduction (41% at 20 mg/kg body weight) in the frequency of micronuclei induced by 1 Gy gamma-rays. Reduction was observed in cells sampled at 24, 30 and 48 h postirradiation with no apparent effect on the ratio of poly- to normo-chromatic erythrocytes in BSO-treated versus control groups. Glutathione levels in the bone marrow of BSO-treated animals 2 h after a single injection were found to be unaltered. The protective effect of BSO was not observed if it was given either immediately or 2 h after irradiation. Based on these and earlier findings it seemed as if BSO molecules may be involved in physicochemical reactions with reactive species generated in the system by irradiation. BSO showed relatively high reaction rate constants with hydroxyl radical (.OH, 2.5 x 10(9) dm3 mol-1s1, calculated on the basis of competition kinetics) and with singlet oxygen (1O2, 4.3 x 10(7) dm3 mol-1s-1 but a lower rate constant with hydrated electrons (< or = 5.0 x 10(6) dm3 mol-1s1). Based on half-life estimates, transients formed and potential for damage to biomolecules, .OH and 1O2 seemed to be the possible species responsible. In vitro studies reveal that BSO has significant abilities to protect DNA against single-strand breaks and lipid peroxidation induced by 1O2 in microsomal membranes. This supports our hypothesis that BSO may be involved in scavenging the reactive species generated and that besides .OH, 1O2 may also be a major player in radiation damage.

Animals↗
PubMed1994

Addition of e-aq and H atoms to hypoxanthine and inosine and the reactions of alpha-hydroxyalkyl radicals with purines. A pulse radiolysis and product analysis study.

The reactions of hydrated electrons e-aq with hypoxanthine and inosine were followed using pulse radiolysis methods. In a neutral solution the electron adduct of inosine is immediately protonated at the heteroatoms of the purine ring by water (k >> 2.5 x 10(6)s-1) to give In(N,O-H).. These N,O-protonated intermediates have a single absorption maximum at 300 nm. In basic solution the protonation of the electron adduct of inosine by water leads to other intermediate products with an absorption maximum at 350 nm. These intermediates are believed to be the C-protonated electron adducts of inosine (In(N,O-H).). In (N,O-H). and In(C-H). differ strongly in their ability to reduce p-nitroacetophenone (PNAP). In(N,O-H). are strong reductants and reduce PNAP quantitatively to PNAP.-. Based on the pH dependence of PNAP.- yields, two types of tautomers of In(C-H). could be distinguished. One of the tautomers can reduce PNAP, albeit with slower rate than In(N,O-H)., the other tautomer has no reducing properties. The latter is the one with the higher pKa and therefore thermodynamically more stable. The absorption spectrum of the intermediates produced in the reaction of e-aq with hypoxanthine at neutral pH is very similar to that of In(N,O-H). with a maximum at 300 nm. However, no build-up at 350 nm was observed in basic solution as in the case of the electron adduct of inosine. The reaction of H atoms with inosine produces in basic solution intermediate radicals with the same absorption spectrum as the C-protonated electron adducts of inosine. It is suggested that both the reactions of e-aq and H. with inosine in basic solution produce the same radical, namely the H-adduct of inosine (In(C-H)) with the highest pKa. alpha-Hydroxyalkyl radicals were found to react very slowly with purine bases and nucleosides in neutral to basic solutions. In acidic solution their reactivity increases and a number of rate constants were determined by pulse radiolysis measurements at pH 0.4. The intermediates from the reaction of 2-hydroxy-2-propyl radicals with inosine could be observed pulse spectrometrically in neutral and in basic solutions. In basic solution this reaction leads to intermediates with the same absorption maximum at 350 nm as that of the H-adduct of inosine. Furthermore, the yield of acetone was found to increase strongly in basic pH.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetophenones↗