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Biomedical subjects

R Gokhale

Publications and source records attributed to R Gokhale.

15 recordsLinked to original sources
PubMed2001

Crystal structure of the macrocycle-forming thioesterase domain of the erythromycin polyketide synthase: versatility from a unique substrate channel.

As the first structural elucidation of a modular polyketide synthase (PKS) domain, the crystal structure of the macrocycle-forming thioesterase (TE) domain from the 6-deoxyerythronolide B synthase (DEBS) was solved by a combination of multiple isomorphous replacement and multiwavelength anomalous dispersion and refined to an R factor of 24.1% to 2.8-A resolution. Its overall tertiary architecture belongs to the alpha/beta-hydrolase family, with two unusual features unprecedented in this family: a hydrophobic leucine-rich dimer interface and a substrate channel that passes through the entire protein. The active site triad, comprised of Asp-169, His-259, and Ser-142, is located in the middle of the substrate channel, suggesting the passage of the substrate through the protein. Modeling indicates that the active site can accommodate and orient the 6-deoxyerythronolide B precursor uniquely, while at the same time shielding the active site from external water and catalyzing cyclization by macrolactone formation. The geometry and organization of functional groups explain the observed substrate specificity of this TE and offer strategies for engineering macrocycle biosynthesis. Docking of a homology model of the upstream acyl carrier protein (ACP6) against the TE suggests that the 2-fold axis of the TE dimer may also be the axis of symmetry that determines the arrangement of domains in the entire DEBS. Sequence conservation suggests that all TEs from modular polyketide synthases have a similar fold, dimer 2-fold axis, and substrate channel geometry.

Amino Acid Sequence↗
PubMed2001

6-mercaptopurine metabolite levels in children with inflammatory bowel disease.

OBJECTIVES: Some authors suggest that efficacy of 6-mercaptopurine (6-MP) in patients with inflammatory bowel disease correlates with circulating 6-thioguanine (6-TG) levels more than 235 pmol/8 x 10(8) red blood cells. The authors evaluated the relation between 6-MP metabolite levels and disease activity in children and adolescents with inflammatory bowel disease. METHODS: Clinical status and hematologic and hepatic parameters were determined in 101 children with inflammatory bowel disease from a single center and compared with 6-MP metabolite levels. RESULTS: There was a trend for higher 6-TG levels among patients in remission than among those with active disease (217 vs. 173); however the difference was not statistically significant ( P = 0.09). The likelihood of therapeutic response did not increase significantly at 6-TG levels greater than 235 pmol/8 x 10(8) red blood cells (odds ratio 1.7; P = 0.1). In the current study, 58% of patients in remission had 6-TG levels less than 235. However, serial measurements of 6-MP metabolite levels in 50 patients with active disease showed that increasing 6-TG levels correlated significantly with disease remission in patients followed up longitudinally ( P = 0.04). Leukopenia was significantly associated with high 6-TG levels ( P = 0.03) but not with clinical response ( P = 0.2). CONCLUSIONS: These data suggest that the target range of 6-TG levels previously described by others did not apply to 58% of the pediatric patients with IBD in remission. However, serial monitoring of 6-MP metabolite levels in individual patients with active disease should allow dose escalation and induction of remission while minimizing the risk of toxicity.

Adolescent↗
PubMed1998

Bone mineral density assessment in children with inflammatory bowel disease.

BACKGROUND & AIMS: Children with inflammatory bowel disease (IBD) are at risk for osteoporosis because of undernutrition, delayed puberty, and prolonged corticosteroid use. The aim of this study was to compare bone mineral density (BMD) in children with IBD with that in normal children and to assess the effects of nutritional and hormonal factors and corticosteroid dosages on BMD. METHODS: One hundred sixty-two subjects (99 with IBD and 63 healthy sibling controls) were enrolled. Patients underwent anthropometric assessment, pubertal staging, bone age radiography, and BMD assessment by dual energy x-ray absorptiometry of the lumbar spine, femoral neck, and radius. Laboratory evaluations included serum calcium, phosphate, alkaline phosphatase, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, parathyroid hormone, osteocalcin, urinary N-telopeptides, albumin, insulin-like growth factor I, and testosterone or estradiol. Cumulative corticosteroid doses were calculated. RESULTS: BMD Z scores at the lumbar spine and femoral neck were lower in patients with IBD, and lower in those with Crohn's disease compared with those with ulcerative colitis. Low BMD persisted after correction for bone age in girls with Crohn's disease (lumbar spine, P = 0.004; femoral neck, P = 0.002). Cumulative corticosteroid dose was a significant predictor of reduced BMD. BMD did not correlate with measures of calcium homeostasis, except elevated serum phosphate and urine calcium levels in girls. CONCLUSIONS: Low BMD occurs in children with IBD (more in Crohn's disease than in ulcerative colitis), especially pubertal and postpubertal girls. Cumulative corticosteroid dose is a predictor of low BMD, but other factors in Crohn's disease remain undetermined.

Adolescent↗
PubMed1997

Use of barbiturates in the treatment of cyclic vomiting during childhood.

BACKGROUND: Cyclic vomiting is an uncommon disorder that can be described as recurrent, self-limiting, fairly uniform episodes of intractable nausea and vomiting with no identifiable organic cause, separated by symptom-free intervals. There is no established therapeutic regimen for this disorder. METHODS: Fourteen children referred to the Pediatric Gastroenterology Clinic were diagnosed with cyclic vomiting from May 1984 to January 1995. Vomiting, the predominant symptom, was present in all children and was severe enough to require hospitalization in 11. Associated symptoms included abdominal ain, headache, nausea, aura, and fever. Diagnostic studies were done to rule out organic causes as indicated in individual patients. Daily phenobarbital was prescribed in all 14 patients. The dose ranged from 30 to 120 mg/hs, (mean 2 mg.kg-1.day-1), with a median dose of 60 mg/hs [corrected]. Prior therapy with propranolol (3 patients) and butalbital (2 patients) had been ineffective. RESULTS: Eleven patients had complete resolution of their symptoms, and 3 patients had marked improvement in their symptoms with infrequent attacks of reduced severity. The only side effects associated with long-term phenobarbital therapy were behavioral in nature, namely hyperactivity and disruptive behavior at school. CONCLUSIONS: The results of our series of 14 patients, all of whom received barbiturates, support the usefulness of this therapeutic approach. Hence we feel that daily low-dose phenobarbital therapy is a safe and effective therapy in preventing episodes of cyclic vomiting in children.

Adolescent↗
PubMed1995

Dermal inflammation in primates, mice, and guinea pigs: attenuation by second-generation leukotriene B4 receptor antagonist, SC-53228.

Granulocyte infiltration is a prominent feature of human psoriasis. Psoriatic lesional skin contains abnormally high amounts of immunoreactive leukotriene B4 (LTB4), a potent granulocyte chemotaxin in vivo and in vitro. SC-53228 [(+)-(S)-7-(3-}2-(cyclopropylmethyl)-3-methoxy-4- [(methylamino)carbonyl]phenoxy}propoxy}-3,4-dihydro-8-propyl-2H-1- benzopyran-2-propanoic acid], a second-generation LTB4 receptor antagonist, was tested topically and orally in phorbol ester-induced dermal inflammation in three species. Skin inflammation was induced by topical application of phorbol-12-myristate-13-acetate-(PMA/TPA) and assessed by ear thickness, levels of the neutrophil marker enzyme myeloperoxidase (MPO) and histological examination. In mice, SC-53228 inhibited inflammation with a topical ED50 value of 200 +/- 18 micrograms. When applied to guinea pigs, SC-53228 (100 micrograms) inhibited the MPO increase by 86%, while 1000 micrograms abrogated inflammation in rhesus macaques with no plasma accumulation of the drug. A 1% gel formulation was also efficacious in guinea pig PMA-induced epidermal inflammation. Furthermore, single oral dose administration to mice was efficacious (ED50 < 2.5 mg/kg) as was multidose administration to rhesus macaques. PMA-induced skin inflammation possesses some of the attributes of human psoriasis and an agent such as SC-53228 may have utility in the medical management of this condition.

Administration, Cutaneous↗
PubMed1992

Ester and amide prodrugs of ibuprofen and naproxen: synthesis, anti-inflammatory activity, and gastrointestinal toxicity.

Ester and amide prodrugs of ibuprofen (1) and naproxen (16) were synthesized and evaluated for anti-inflammatory activity and gastrointestinal toxicity. The chemical structure of the prodrugs was varied in terms of lipophilicity and reactivity toward hydrolysis. Inhibition of acetic acid-induced writhing in mice indicated that prodrugs 7, 15, 19, and 20 exhibited significantly better activity (p less than 0.01) than the parent compounds. The average number of ulcers formed in the gastric mucosa following oral administration of 1 and 16 and prodrugs 5, 18, 21, and 22 was determined in rats. All prodrugs, except the glycine amide 21, were significantly less irritating to the gastric mucosa than either 1 or 16.

Amides↗
PubMed1992

Transdermal drug delivery systems of albuterol: in vitro and in vivo studies.

In vitro and in vivo experiments were conducted with double- and single-layer albuterol transdermal pads designed for once-a-day application. In the in vitro experiments, dissolution of albuterol from pads and permeation of albuterol through hairless mouse skin were monitored. In the in vivo experiments, pads were applied to the chest area of four female rhesus monkeys (Macaca mulata), and an albuterol aqueous solution was injected into the saphenous vein of the same animals in a crossover design. The amount lost from pads applied to monkeys was monitored by analysis of pad residue. Blood samples were withdrawn at regular intervals and analyzed by a high-performance liquid chromatography-fluorescence method. Skin irritation due to the pad was measured by a modified Draize score test. The amounts released from the two formulations were similar. The amount released was, however, dependent on the technique used and decreased in the following manner: pad dissolution greater than in vivo amount lost from pads applied to monkeys greater than in vitro permeation through hairless mouse skin. The pharmacokinetic parameters determined after intravenous and transdermal administration were as follows: terminal half-life, 2.26 +/- 0.45 h; apparent volume of distribution, 1935 +/- 37.2 mL.kg-1; and total body clearance, 612.0 +/- 118 mL.h-1.kg-1. The average concentrations in serum after application of single- and double-layer pads were 44.60 +/- 16.40 and 62.50 +/- 8.00 ng/mL, respectively. Further, the amount lost from pads applied to monkeys correlated with the respective amount absorbed in monkeys, as calculated from the average concentration in serum and clearance.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Cutaneous↗
PubMed1990

Hydrolysis of nipecotic acid phenyl esters.

The synthesis and anticonvulsant activity of nipecotic acid esters (1a-1f) have been previously reported. It was thought that these prodrug esters underwent hydrolytic conversion to 1 which inhibited GABA uptake, and that both 1 and an intact ester may have caused inhibition of GABA uptake which resulted in the anticonvulsant activity. There is, however, no stability data available to help evaluate these effects. We have determined degradation half-lives (t 1/2) of these phenyl esters dissolved in 10% serum solution or in pH 7.4 buffer (ionic strength = 0.25 adjusted with KCl) at 37 degrees C by monitoring the appearance of a phenolic compound for a period of 12 h with an HPLC method. Utilizing a published method, in vitro [14C]GABA uptake was measured. Results show that the hydrolysis rate in 10% serum solution was faster than that in buffer solution and that half-lives varied between 0.20 and 3.84 h. The uptake inhibition varied between 8.2 and 41.7% at 0.02 mM concentration, and percent GABA uptake inhibition correlated with log t 1/2 (r = -0.9827, p = 0.00045, based on a t test). Our data suggest that at concentrations ranging from 0.02 to 1 mM, inhibition of GABA uptake is mainly due to 1 formed after hydrolysis of 1a-1f.

Animals↗
PubMed1985

Intraoperative ceforanide pharmacokinetics and protein binding.

The pharmacokinetics and protein binding of ceforanide were studied in 15 patients undergoing cholecystectomies. Each patient received ceforanide (20 mg/kg) intravenously on arrival in the operating room, after which serial blood samples were collected during the elimination phase for determination of total and free ceforanide concentrations in the serum. A high-pressure liquid chromatography assay was used, with a centrifugal filtration system for free-drug determinations. Serum concentration data for each individual were subjected to linear regression to determine the elimination rate constants (total and free drug), volumes of distribution, and systemic clearances. The mean elimination rate constants were 0.41 and 0.50 h-1 for total and free ceforanide, respectively. The mean percentage of ceforanide bound to serum protein was 87.9%. The relationship of the free ceforanide concentration to the total concentration appeared to be linear. The data were fit to double-reciprocal and half-reciprocal relationships with good agreement, showing one binding site and an association constant range of 1.6 X 10(7) to 1.9 X 10(7) at these in vivo concentrations. The mean volume of distribution and mean systemic clearance of total drug were 100 ml/kg and 45.9 ml/min per 1.73 m2, respectively. Ceforanide consistently produced higher intraoperative total drug concentrations compared with those of cefazolin and cefoxitin from similar studies.

Adolescent↗