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Biomedical subjects

A Trehan

Publications and source records attributed to A Trehan.

At least 37 records · Page 2Linked to original sources
PubMed1998

Recent approaches in insulin delivery.

Insulin remains indispensable in the management of diabetes mellitus since its discovery in 1921. The foreignness of early available porcine and bovine insulin led to the development of human insulin by transpeptidation and biosynthesis in microorganisms. Needle phobia and stress of multiple daily injections led to the investigation and exploitation of all promising routes, ranging from nasal to rectal, by a wide variety of devices and delivery systems. This article describes the development of human insulin, various routes for delivery of insulin (including oral, nasal, buccal, rectal, and pulmonary), and various devices for regulated, safe, and convenient insulin delivery. The article reviews some recent advances in insulin delivery such as the bioresponsive and self-regulated insulin delivery system.

Administration, Inhalation↗
PubMed1995

Active site-directed thrombin inhibitors--II. Studies related to arginine/guanidine bioisosteres.

A series of N-arylsulfonylarginine amides was synthesized wherein the guanidine or arginine moiety was isosterically replaced by a number of heterocyclic functionalities. These compounds were evaluated as potential active-site inhibitors of thrombin. Bisamidines 11a-n showed a similar SAR to that of simple arginine compounds. The ex vivo clotting time measurement of 11d after ip dosing showed prolongation of clotting time in rats.

Animals↗
PubMed1995

A study comparing LETZ and CO2 laser treatment for cervical intra epithelial neoplasia with and without associated human papilloma virus.

OBJECTIVE: To evaluate the recurrence of cervical intraepithelial neoplasia (CIN) following treatment with CO2 laser ablation and loop excision of the transformation zone (LETZ) and its correlation with the presence of HPV. METHODS: Six hundred and forty two women diagnosed as having CIN were treated either by CO2 laser (318) or LETZ (324) and were followed up for a minimum of 12 months. Recurrence rates in each group were evaluated and correlated with the presence or absence of HPV prior to treatment. RESULTS: There was a considerably higher rate of recurrent disease observed after treatment with laser ablation than LETZ (9% after LETZ and 37% after laser ablation) p < 0.001. Two hundred and sixty four women (41%) had HPV infection prior to treatment and 29% of these required further treatment for recurrent CIN whereas there were only 11% of women out of the 374 who had no evidence of HPV infection p < 0.001. CONCLUSION: Treatment of CIN in the presence of HPV infection results in higher failure rates and this is significantly increased when the treatment is by laser ablation rather than by LETZ.

Adolescent↗
PubMed1990

Comparative study on the chromophore binding sites of rod and red-sensitive cone visual pigments by use of synthetic retinal isomers and analogues.

A comparative study on the chromophore (retinal) binding sites of the opsin (R-photopsin) from chicken red-sensitive cone visual pigment (iodopsin) and that scotopsin) from bovine rod pigment (rhodopsin) was made by the aid of geometric isomers of retinal (all-trans, 13-cis, 11-cis, 9-cis, and 7-cis) and retinal analogues including fluorinated (14-F, 12-F, 10-F, and 8-F) and methylated (12-methyl) 11-cis-retinals. The stereoselectivity of R-photopsin for the retinal isomers and analogues was almost identical with that of scotopsin, indicating that the shapes of the chromophore binding sites of both opsins are similar, although the former appears to be somewhat more restricted than the latter. The rates of pigment formation from R-photopsin were considerably greater than those from scotopsin. In addition, all the iodopsin isomers and analogues were more susceptible to hydroxylamine than were the rhodopsin ones. These observations suggest that the retinal binding site of iodopsin is located near the protein surface. On the basis of the spectral properties of fluorinated analogues, a polar group in the chromophore binding site of iodopsin as well as rhodopsin was estimated to be located near the hydrogen atom at the C10 position of the retinylidene chromophore. A large difference in wavelength between the absorption maxima of iodopsin and rhodopsin was significantly reduced in the 9-cis and 7-cis pigments. On the assumption that the retinylidene chromophore is anchored rigidly at the alpha-carbon of the lysine residue and loosely at the cyclohexenyl ring, each of the two isomers would have the Schiff-base nitrogen at a position altered from that of the 11-cis pigments.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Inhibitors of retinyl ester formation also prevent the biosynthesis of 11-cis-retinol.

Lecithin retinol acyl transferase (LRAT) from the retinyl pigment epithelium is potently inhibited by all-trans-retinyl alpha-bromoacetate in the micromolar range. The inhibition is competitive and reversible. The retinyl pigment epithelium also contains an enzymatic activity capable of converting added all-trans-retinol into 11-cis-retinol. This isomerization is likely to require the intermediate formation of all-trans-retinyl esters, which are themselves produced by LRAT action. Here this possibility is directly tested by studying the effect of all-trans-retinyl alpha-bromoacetate on the isomerization reaction. When pigment epithelium membranes are preincubated with all-trans-retinyl alpha-bromoacetate, they form neither retinyl esters nor 11-cis-retinol from added all-trans-retinol. However, if the pigment epithelium membranes are first allowed to form all-trans-retinyl esters from all-trans-retinol before the addition of all-trans-retinyl alpha-bromoacetate, then 11-cis-retinol formation proceeds at close to the rate found in the absence of inhibitor. In addition, 11-cis-retinyl esters are not formed under these conditions, eliminating the possibility of a direct ester-ester isomerization route. Therefore, all-trans-retinyl esters are obligate intermediates in the biosynthesis of 11-cis-retinol.

Acyltransferases↗
PubMed1988

9,13-dicis-rhodopsin and its one-photon-one-double-bond isomerization.

Incubation of purified 9,13-dicis-retinal with cattle opsin in 2% digitonin at 20 degrees C produced two pigments, one unstable (lambda max 478 nm) and the other stable (lambda max 485 nm) in hydroxylamine. The two pigments exhibited different characteristics. HPLC analysis revealed that the chromophores of these pigments have respectively 9,13-dicis and 9-cis geometries. Under various conditions the amount of 9,13-dicis-rhodopsin formed never exceeded 30% of the total pigments. The addition of 9,13-dicis-retinal to the ROS suspension containing opsin produced 9-cis-rhodopsin in 97% yield. Irradiation of the 9,13-dicis-rhodopsin mainly produced 13-cis-retinal, while 9-cis-rhodopsin produced the all-trans isomer. These results demonstrated that the one-photon-one-double-bond isomerization process took place in 9,13-dicis-rhodopsin.

Animals↗