Biomedical subjects

S Govindaraj

Publications and source records attributed to S Govindaraj.

15 recordsLinked to original sources

PubMed2001

Facial purpura.

OBJECTIVES: Patients with facial purpura can have acute and dramatic illnesses. For this reason, the clinician must be aware of certain diagnoses that can present as facial purpura and know how to initiate treatment efficiently. According to our review of the literature, no paradigm currently exists for the diagnosis and management of facial purpura Our goal is to develop a schema for the identification and management of facial purpura. STUDY DESIGN: Case series. METHODS: A case series of five cases is presented followed by a systematic development of a differential diagnosis based on etiology of the lesion. RESULTS: Facial purpura can be classified into conditions that are primarily or secondarily vasculitic, thrombocytopenic, neoplastic, infectious, toxic, and miscellaneous, which encompasses episodic reports that do not fit into the other categories. A paradigm to diagnose patients with facial purpura is developed based on clinical presentation and etiology. To demonstrate the utility of our algorithm, the five cases presented are re-examined using the algorithm. To our knowledge, this represents the first reported series of facial purpura in the modern English literature. A flow chart based on our diagnostic paradigm is presented. CONCLUSION: Clinicians caring for patients with facial purpura must recognize the acute conditions that require emergent medical intervention. Once these diagnoses have been considered, the clinician can employ a systematic approach to the diagnosis based on etiology. This study provides a useful reference for the otolaryngologist when encountering a patient with facial purpura.

Adult↗

PubMed2001

Tympanic membrane repair with a dermal allograft.

OBJECTIVES: To assess the use of an acellular dermal allograft in the repair of chronic tympanic membrane perforations. Chronic tympanic membrane perforations are a common problem in otolaryngology, and although surgical tympanoplasty using either temporalis fascia or rice paper has proven to be highly successful, these materials are not without their own limitations. The search has continued for a simpler, yet equally effective, means of repairing persistent tympanic membrane perforations in an office setting. In this study we experimentally evaluated the use of an acellular dermis (AlloDerm, (LifeCell Corporation, The Woodlands, TX) as an alternative to traditional tympanoplasty materials. STUDY DESIGN: Prospective study using 28 adult chinchillas. METHODS: Subtotal tympanic membrane perforations were created bilaterally in 28 adult chinchillas. Animals with noninfected, stable perforations that showed no signs of epithelial regeneration after 5 to 8 weeks were used to compare the use of rice paper patch with AlloDerm in patch tympanoplasties. RESULTS: Eighteen of 23 tympanoplasties (78%) that were performed using AlloDerm showed no signs of perforation after 5 to 6 weeks. In those performed using rice paper control, 14 of 21 (66%) showed no signs of perforation after 5 to 6 weeks. In addition, histological evaluation of the healed tympanic membranes demonstrated that the acellular dermis had been incorporated within the middle fibrous layer of the tympanic membrane. CONCLUSIONS: The results and histological studies suggest that acellular dermis may be a suitable alternative to traditional materials currently used for patch tympanoplasty. Future studies to evaluate the efficacy of acellular dermis in humans are warranted.

Animals↗

PubMed2001

The use of acellular dermis in the prevention of Frey's syndrome.

EDUCATIONAL OBJECTIVE: At the conclusion of this presentation, the participant should be able to discuss the indications and advantages of using acellular dermis in the prevention of post-parotidectomy gustatory sweating (Frey's Syndrome). INTRODUCTION: Gustatory sweating is a common postoperative problem and a challenge to treat. The purpose of this study was to evaluate the role of acellular dermis in preventing post-parotidectomy gustatory sweating. METHODS: Sixty-four patients were randomly assigned to two groups. Group I consisted of 32 patients who underwent a superficial lobe parotidectomy. Group II consisted of 32 patients who underwent a superficial lobe parotidectomy and underwent intraoperative placement of acellular dermis within the parotid bed, between the skin flap and the remaining parotid tissue. The implanted volume of acellular dermis was determined by the amount required to aesthetically restore lateral facial contour. All 64 patients were evaluated for gustatory sweating by identical phone and mail questionnaires. Thirty randomly chosen patients (group I = 15, group II = 15) were evaluated using a modified Minor's Starch-Iodine Test (MSIT). In all 30 patients, the MSIT was administered to both sides of the face. RESULTS: The responses to questionnaires (N = 64) demonstrated the subjective presence of gustatory sweating in 3 of 32 patients (9.3%) in group I, whereas group II demonstrated a subjective incidence in 1 of 32 patients (3.1%). The objective incidence determined by those who underwent the MSIT (n = 30) revealed a 40% (6) and 0% incidence of Frey's Syndrome in groups I and II, respectively. The complication rate in group I was 9% (3 seromas) and in group II it was 25% (7 seromas and 1 wound infection). CONCLUSIONS: Acellular dermis appears to be an effective method for preventing post-parotidectomy gustatory sweating, despite its higher complication rate.

Biocompatible Materials↗

PubMed2000

Human dural replacement with acellular dermis: clinical results and a review of the literature.

BACKGROUND: The search for the ideal dural replacement in the setting where autogenous tissues are unavailable or inadequate still persists. Because of the ability of acellular dermis (AlloDerm, LifeCell Corporation, The Woodlands, TX) to remodel itself into native tissue, this dynamic quality is hypothesized to occur when used as a dural replacement. METHODS: We report the long-term outcome of a small cohort of patients who, to our knowledge, were the first patients to receive AlloDerm for dural replacement. In addition, to put these current findings in a historical perspective, we present a review of the literature for dural replacement. RESULTS: Ten patients all successfully underwent duraplasty with AlloDerm with only one postoperative complication that was not related to the acellular dermal dural repair. CONCLUSIONS: We contend that AlloDerm is a safe and viable option for dural replacement in cases in which autogenous tissues are either unavailable or insufficient for proper reconstruction.

Adult↗

PubMed2000

Applications of fast-setting hydroxyapatite cement: cranioplasty.

A variety of autogenous and synthetic materials have been used to repair cranial defects resulting from traumatic and iatrogenic causes. In theory, the ideal material should be readily available and safe. It should adequately protect the underlying central nervous system, resist cerebrospinal fluid fistula formation, and be easily contoured. One promising synthetic biomaterial that has been used for cranioplasty is hydroxyapatite cement. This biomaterial has successfully restored cranial contour in most patients in whom it has been used; however, difficulties have arisen because of the material's prolonged water solubility. When exposed to cerebrospinal fluid or blood, inadequate setting of the cement occurs, resulting in loss of its structural integrity. This problem can be alleviated with the use of fast-setting hydroxyapatite cement, which hardens 6 to 12 times faster than the traditional cement. We present, to the best of our knowledge, the first series of the use of this material in 21 patients requiring cranioplasty. The advantages and limitations of fast-setting hydroxyapatite cement will be discussed.

Adult↗

PubMed2000

A meta-analysis of dexamethasone use with tonsillectomy.

OBJECTIVE: To determine the quantitative impact of intravenous dexamethasone on recovery after tonsillectomy using established principles for meta-analysis. STUDY DESIGN/SETTING: Double-blind randomized-control trials in which subjects were treated identically except for the presence or absence of perioperative intravenous dexamethasone. Six articles met inclusion criteria. Two investigators extracted data regarding postoperative emesis and return to a soft/regular diet. RESULTS: Pooled analysis using a random effects model revealed a 27% decrease (P<0.00001) in postoperative emesis attributable to dexamethasone (95% CI, 12% to 42%). Dexamethasone increased the tolerance of a soft/regular diet at 24 hours by 22% (P< 0.001), but studies were heterogenous with low precision (95% CI, 1% to 44%). CONCLUSION: To prevent emesis in 1 child after tonsillectomy, approximately 4 children must receive perioperative dexamethasone. An additional benefit is earlier tolerance of a soft/regular diet, but low precision and heterogeneity among studies preclude definitive conclusions. SIGNIFICANCE: Perioperative dexamethasone administration had a positive impact on recovery from tonsillectomy.

Antiemetics↗

PubMed1999

Current use of bone substitutes in maxillofacial surgery.

The use of bone substitutes in the field of facial plastic and reconstructive surgery is well established. Because of the complexity of the anatomy in the head and neck region, reconstruction and augmentation of this area pose a challenge to the surgeon. In addition, the shortcomings of autogenous bone, such as resorption and donor site morbidity, have led to the need for alloplastic implants in the field of facial plastic surgery. Multiple alloplastic implants are currently in use today; however, those compounds that contain calcium, silicon, and carbon have been examined more closely in this article. This is because of their ability to osseointegrate and osseoconduct with surrounding fibro-osseous tissue, as well as demonstrate a higher immunogenic tolerance by the human body. The discussion of each compound includes a description of its composition and structure, the advantages and shortcomings of the material, and its current uses in the field of facial plastic and reconstructive surgery. With a better understanding of the available alloplastic implants, the surgeon can make a more informed decision as to which implant would be most suitable in a particular patient.

Bone Morphogenetic Protein 3↗

PubMed1997

Redox control of the catalytic cycle of flavocytochrome P-450 BM3.

Flavocytochrome P-450 BM3 from Bacillus megaterium is a 119 kDa polypeptide whose heme and diflavin domains are fused to produce a catalytically self-sufficient fatty acid monooxygenase. Redox potentiometry studies have been performed with intact flavocytochrome P-450 BM3 and with its component heme, diflavin, FAD, and FMN domains. Results indicate that electron flow occurs from the NADPH donor through FAD, then FMN and on to the heme center where fatty acid substrate is bound and monooxygenation occurs. Prevention of futile cycling of electrons is avoided through an increase in redox potential of more than 100 mV caused by binding of fatty acids to the active site of P-450. Redox potentials are little altered for the component domains with respect to their values in the larger constructs, providing further evidence for the discrete domain organization of this flavocytochrome. The reduction potentials of the 4-electron reduced diflavin domain and 2-electron reduced FAD domain are considerably lower than those for the blue FAD semiquinone species observed during reductive titrations of these enzymes and that of the physiological electron donor (NADPH), indicating that the FAD hydroquinone is thermodynamically unfavorable and does not accumulate under turnover conditions. In contrast, the FMN hydroquinone is thermodynamically more favorable than the semiquinone.

Bacillus megaterium↗

PubMed1997

The domain architecture of cytochrome P450BM-3.

Cytochromes P450 utilize redox partners to deliver electrons from NADPH/NADH to the P450 heme center. Microsomal P450s utilize an FAD/FMN reductase. The bacterial fatty acid hydroxylase, P450BM-3, is similar except the P450 heme and FAD/FMN proteins are linked together in a single polypeptide chain arranged as heme-FMN-FAD. Sequence comparisons indicate that the P450BM-3 FMN and FAD domains are similar to flavodoxin and ferredoxin reductase, respectively. Previous work has shown that the heme and FMN/FAD domains can be separately expressed and purified. In this study we have expressed, purified, and characterized the following additional domains: heme-FMN, FMN, and FAD. Each domain retains their prosthetic groups although the FMN domain is more labile. The FAD domain retains a high level of ferricyanide reductase activity but no cytochrome c reductase activity. In addition, we have deleted a 110-residue stretch in the FAD domain that is not present in ferredoxin reductase. This protein retains both FAD and heme but not FMN. We also have investigated the dimerization pattern of the individual domains that lead to the following conclusions. Holo-P450BM-3 appears to dimerize via interactions that do not involve disulfide bond formation, whereas the reductase and FAD domains form intermolecular disulfides. This indicates that the Cys residues not available for dimerization in holo-P450BM-3 are unmasked in the individual domains.

Amino Acid Sequence↗

PubMed1997

Electron transfer between the FMN and heme domains of cytochrome P450BM-3. Effects of substrate and CO.

Cytochrome P450BM-3 has the P450 heme domain and FAD/FMN reductase domain linked together in a single polypeptide chain arranged as heme-FMN-FAD. In the accompanying article (Govindaraj, S., and Poulos, T. L. (1997) J. Biol. Chem. 272, 7915-7921, we have described the preparation and characterization of the various domains of cytochrome P450BM-3. One reason for undertaking this study was to provide simpler systems for studying intramolecular electron transfer reactions. In particular, the heme-FMN version of P450BM-3 that is missing the FAD domain should prove useful in studying the FMN-to-heme electron transfer reaction. This version of P450BM-3 has been designated truncated P450BM-3 or BM3t. In this study we have used laser flash photolysis techniques to generate the reduced semiquinone of 5-deazariboflavin which in turn reduces the FMN of BM3t to the semiquinone, FMN-, at a rate constant of 6600 s-1, whereas the heme is not reduced by the 5-deazariboflavin radical. The reduction of the heme by FMN- does not proceed in the absence of carbon monoxide (CO), whereas in the presence of CO the FMN- to heme electron transfer rate constant is 18 s-1. If a fatty acid substrate is present, this rate constant increases to 250 s-1. Somewhat surprisingly, the rate of heme reduction also is dependent on [CO] which indicates that CO causes some change within the heme pocket and/or interaction between the heme and FMN domains that is required for intramolecular electron transfer.

Bacterial Proteins↗

PubMed1996

Probing the structure of the linker connecting the reductase and heme domains of cytochrome P450BM-3 using site-directed mutagenesis.

Cytochrome P450BM-3 is a catalytically self-sufficient fatty acid hydroxylase containing one equivalent each of heme, FMN, and FAD. The heme and flavins reside in separate domains connected by a linker peptide. In an earlier study (Govindaraj S, Poulos T, 1995, Biochemistry 34:11221-11226), we found that the length but not the sequence of the linker connecting the heme and reductase domains is important for enzyme activity. In the present study, residues in the linker were replaced with Pro and Gly to probe the role that regular secondary structure plays in linker function. The rate of flavin-to-heme electron transfer and the fatty acid hydroxylase activities of the glycine and proline substitution mutants, including a six-proline substitution, did not change significantly relative to wild-type enzyme. These results indicate that the linker does not adopt any regular secondary structure essential for activity and that the length of the linker is the critical feature that controls flavin-to-heme electron transfer.

Bacterial Proteins↗

PubMed1995

Role of the linker region connecting the reductase and heme domains in cytochrome P450BM-3.

Cytochrome P450BM-3 is a fatty acid monooxygenase that contains the catalytic P450 heme domain covalently attached to a diflavin P450 reductase domain. The function of the linker region connecting the C-terminal end of the heme domain to the N-terminal end of the reductase domain has been studied by deleting parts of the linker and changing the sequence of the linker. Deleting three or six residues or changing an Arg-Lys-Lys stretch in the middle of the linker to Ala-Ala-Ala does not alter the functional properties of either domain. The mutants retain full cytochrome c and ferricyanide reductase activities characteristic of the P450 reductase domain. The heme domain in the mutants retains its ability to bind a fatty acid substrate giving the full low-to-high spin shift and exhibits the normal 450 nm absorption band characteristic of the reduced carbon monoxide complex. However, the six amino acid deletion mutant exhibit nearly undetectable levels of fatty acid hydroxylase activity, the three amino acid deletion mutant about 10% activity, and the three Ala substitution mutant about 50% activity. The mutants also exhibit slower rates of reductase-to-heme electron transfer rates that correlate with the loss in fatty acid hydroxylase activity. These results indicate that the length of the linker and, to a much less extent, the sequence are important for correctly orienting the reductase and heme domains, which apparently is necessary to achieve efficient reductase-to-heme electron transfer rates.

Amino Acid Sequence↗

PubMed1994

Aromatic amine dehydrogenase, a second tryptophan tryptophylquinone enzyme.

Aromatic amine dehydrogenase (AADH) catalyzes the oxidative deamination of aromatic amines including tyramine and dopamine. AADH is structurally similar to methylamine dehydrogenase (MADH) and possesses the same tryptophan tryptophylquinone (TTQ) prosthetic group. AADH exhibits an alpha 2 beta 2 structure with subunit molecular weights of 39,000 and 18,000 and with a quinone covalently attached to each beta subunit. Neither subunit cross-reacted immunologically with antibodies to the corresponding subunits of MADH, and the N-terminal amino acid sequence of the beta subunit of AADH exhibited no homology with the highly conserved beta subunits of MADH. The absorption spectra for the oxidized, semiquinone, and reduced forms of AADH have been characterized, and extinction coefficients for the absorption maxima of each redox form have been determined. These spectra are very similar to those for MADH, indicating the likelihood of a TTQ cofactor. This was verified by the near identity of the vibrational frequencies and intensities in the resonance Raman spectra for the oxidized forms of AADH and MADH. A stable semiquinone of AADH could be observed during a reductive titration with dithionite, whereas titration with tyramine proceeded directly from the oxidized to the reduced form. AADH was very stable against denaturation by heat and exposure to guanidine. The individual subunits could be separated by gel filtration after incubation in guanidine hydrochloride, and partial reconstitution of activity was observed on recombination of the subunits. Steady-state kinetic analysis of AADH yielded a Vmax of 17 mumol/min/mg and a Km for tyramine of 5.4 microM. Substrate inhibition by tyramine was observed. AADH was irreversibly inhibited by hydrazine, phenylhydrazine, hydroxylamine, semicarbazide, and aminoguanidine. Isonicotinic acid hydrazide (isoniazid) and isonicotinic acid 2-isopropyl hydrazide (iproniazid) were reversible noncompetitive inhibitors of AADH and exhibited K(i) values of 8 and 186 microM, respectively. The similarities and differences between AADH and other amine oxidizing enzymes are also discussed.

Alcaligenes↗

PubMed1976

Placenta, transcortin, and localized immune response.

The syncytiotrophoblastic cells of the human placenta contain a cytoplasmic protein recognized by fluorescein-labeled transcortin-specific antibody. Purification of this protein from human placenta, by those methods employed for the purification of human plasma transcortin, yielded a protein that exhibited antigenic and biochemical similarity to plasma transcortin. Placental transcortin differs from plasma transcortin in that it has a smaller sedimentation coefficient (3S vs 3.75S) and binds cortisol less strongly. This purified protein is able to block the phytohemagglutinin response of maternal lymphocytes even more than serum transcortin. It is postulated that the biological role may be that of inhibiting the maternal cell-mediated immune response to the presence of the antigenic conceptus.

Chromatography, DEAE-Cellulose↗

PubMedDate not supplied

Acellular dermis for facial soft tissue augmentation: preliminary report.

OBJECTIVE: To evaluate the efficacy of acellular dermis as a viable alternative for soft tissue augmentation in facial reconstruction. DESIGN: A prospective, nonrandomized observational study consisting of 10 patients who underwent soft tissue augmentation with acellular dermis. SETTING: A tertiary care university medical center in an urban setting. PATIENTS: Ten patients who had undergone soft tissue augmentation using acellular dermis participated in this study. Postimplantation follow-up was 17 to 36 months. INTERVENTION: The amount and location for placement of the acellular dermis was left to the discretion of the surgeon. All implants were placed in the subdermal tissues. MAIN OUTCOME MEASURES: The adequacy of acellular dermis for soft tissue augmentation was assessed by subjective evaluation of implant volume persistence, postoperative complications, and the restoration of normal contour. RESULTS: Of 10 patients who underwent implantation, 9 had no complications and 1 had a recurrent sterile abscess or mucocele at the implantation site. A 22-month postimplantation tissue sampling of acellular dermis in a patient with recurrent tumor revealed approximately 80% to 85% volume persistence. CONCLUSION: Preliminary experience with acellular dermis indicates that it shows promise in soft tissue augmentation.

Adult↗