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Biomedical subjects

Sandeep Saxena

Publications and source records attributed to Sandeep Saxena.

11 recordsLinked to original sources
PubMed2006

Decreased platelet membrane fluidity in retinal periphlebitis in Eales' disease.

PURPOSE: Oxidative damage to cellular membranes plays an important role in the pathobiology of tissue injury. Free radical-induced peroxidation of membrane lipid and protein is associated with alterations in cellular, morphological, biochemical, and physical dynamics, which are related to the mobility of lipid molecules. Retinal photoreceptors and platelets have been shown to be an easy target of oxidants because of their high proportion of polyunsaturated fatty acids. This study was undertaken, for the first time, to investigate membrane fluidity in the platelets of patients with Eales' disease. METHODS: Assays of malonaldialdehyde levels and the enzymes superoxide dismutase and catalase and fluorescence polarization, for estimating membrane fluidity, were carried out on platelets from 20 patients with Eales' disease (stage 1 characterized by periphlebitis of small (1a) and large (1b) caliber vessels with superficial retinal hemorrhages) and 15 healthy controls. RESULTS: A significant increase was observed in the malonaldialdehyde levels. A significant decrease in the activity of superoxide dismutase and catalase was also observed. Platelet fluorescence polarization was significantly higher in the patients, indicating decreased membrane fluidity compared to controls (p<0.01). CONCLUSION: A decrease in platelet membrane fluidity occurs as a result of oxidative stress in retinal periphlebitis in Eales' disease. The decreased membrane fluidity suggests alterations in the physiological events, which may result in alterations in the functioning of retinal photoreceptors.

Adult↗
PubMed2005

Genetic homogeneity for inherited congenital microcoria loci in an Asian Indian pedigree.

PURPOSE: Congenital microcoria is a rare autosomal dominant developmental disorder of the iris associated with myopia and juvenile open angle glaucoma. Linkage to the chromosomal locus 13q31-q32 has previously been reported in a large French family. In the current study, a three generation Asian Indian family with 15 congenital microcoria (pupils with a diameter <2 mm) affected members was studied for linkage to candidate microsatellite markers at the 13q31-q32 locus. METHODS: Twenty-four members of the family were clinically examined and genomic DNA was extracted. Microsatellite markers at 13q31-q32 were PCR amplified and run on an ABI Prism 310 genetic analyzer and genotyped with the GeneScan analysis. Two point and multipoint linkage analyses were performed using the MLINK and SUPERLINK programs. RESULTS: Peak two point LOD scores of 3.5, 4.7, and 5.3 were found co-incident with consecutive markers D13S154, DCT, and D13S1280. Multipoint analysis revealed a 4 cM region encompassing D13S1300 to D13S1280 where the LOD remains just over 6.0 Thus we confirm localization of the congenital microcoria locus to chromosomal locus 13q31-q32. In addition, eight individuals who had both microcoria and glaucoma were screened for glaucoma genes: myocilin (MYOC), optineurin (OPTN) and CYP1B1. Using direct sequencing a point mutation (144 G>A) resulting in a Q48H substitution in exon 1 of the MYOC gene was observed in five of the eight glaucoma patients, but not in unaffected family members and 100 unrelated controls. CONCLUSIONS: We have confirmed the localization of the congenital microcoria locus (MCOR) to 13q31-q32 in a large Asian Indian family and conclude that current information suggests this is a single locus disorder and genetically homogeneous. When combined with the initial linkage paper our haplotype and linkage data map the MCOR locus to a 6-7 cM region between D13S265 and D13S1280. The DCT locus, a member of the tyrosinase family involved in pigmentation, maps within this region. Data presented here supports the hypothesis that congenital microcoria is a potential risk factor for glaucoma, although this observation is complicated by the partial segregation of MYOC Q48H (1q24.3-q25.2), a mutation known to be associated with glaucoma in India. Fine mapping and candidate gene analysis continues with the hope that characterizing the micocoria gene will lead to a better understanding of microcoria and glaucoma causation. The relationship between microcoria, glaucoma, and the MYOC Q48H mutation in this family is discussed.

Adolescent↗
PubMed2005

Geminin-Cdt1 balance is critical for genetic stability.

A cell limits its DNA replication activity to once per cell division cycle to maintain its genomic integrity. Studies in a variety of organisms are elucidating how these controls are exercised. Key amongst these is the regulation of replication initiator proteins such as Cdt1. Cdt1 is present in cells in G1 phase where it is required for initiation of replication. Once origins have fired, Cdt1 is either exported out of the nucleus or degraded, thereby preventing another round of replication. Higher eukaryotes have evolved another redundant mechanism, an inhibitor called geminin, to restrain Cdt1 activity. Studies in multiple organisms have shown that unregulated Cdt1 activity stimulates overreplication of the genome. Interestingly, the same seems to be true when geminin is depleted. The imbalance in the activities of these proteins causes the activation of key checkpoint proteins, the ATM/ATR kinases and the tumor suppressor, p53. This review proposes that a balance between Cdt1 and geminin is important for maintaining genomic stability.

Animals↗
PubMed2004

A dimerized coiled-coil domain and an adjoining part of geminin interact with two sites on Cdt1 for replication inhibition.

Geminin is a cellular protein that associates with Cdt1 and inhibits Mcm2-7 loading during S phase. It prevents multiple cycles of replication per cell cycle and prevents episome replication. It also directly inhibits the HoxA11 transcription factor. Here we report that geminin forms a parallel coiled-coil homodimer with atypical residues in the dimer interface. Point mutations that disrupt the dimerization abolish interaction with Cdt1 and inhibition of replication. An array of glutamic acid residues on the coiled-coil domain surface interacts with positive charges in the middle of Cdt1. An adjoining region interacts independently with the N-terminal 100 residues of Cdt1. Both interactions are essential for replication inhibition. The negative residues on the coiled-coil domain and a different part of geminin are also required for interaction with HoxA11. Therefore a rigid cylinder with negative surface charges is a critical component of a bipartite interaction interface between geminin and its cellular targets.

Amino Acid Sequence↗
PubMed2004

Human S-antigen: peptide determinant recognition in uveitis patients.

Uveitis is an inflammation of the uveal tract and is one of the major causes of visual impairment. Several lines of evidence suggest an important role for activated T lymphocytes in the perpetuation of posterior uveitis. In sequel to our preliminary observations with human S-antigen, we have further investigated the proliferative response of peripheral blood lymphocytes of posterior uveitis patients against 20 linear and 9 overlapping peptides of retinal S-antigen. The expression of surface markers CD4, CD8, CD29, CD45RA in peripheral blood was detected by flow cytometry. We have also assessed the pattern of cytokines present in peripheral blood mononuclear cells (PBMCs) using ribonuclease protection assay (RPA). Nineteen out of 32 patients' lymphocytes showed proliferative response to S-antigen, one or more of its 20 linear and nine overlapping synthetic peptides. Six patients showed significant lymphoproliferative response against various peptides. The maximum response was found to peptides from the 231-270 amino acid region of human S-antigen sequence. The percentage of CD29(+) (memory cells) and CD45RA(+) (naive cells) T-lymphocytes was higher in patients compared to healthy volunteers. There was a demonstrable difference in the percentage of CD4(+) and CD8(+) lymphocytes in the patients (P <== 0.05) as compared to controls. Higher message for interleukin (IL)-5, IL-10, IL-15, IL-9, IL-2, IL-13, and interferon (IFN)-gamma was observed in uveitis patients than in healthy individuals. In brief, our study suggests that a particular region of S-antigen plays an important role in idiopathic uveitis.

Adolescent↗
PubMed2003

Small RNAs with imperfect match to endogenous mRNA repress translation. Implications for off-target activity of small inhibitory RNA in mammalian cells.

A 21-base pair RNA duplex that perfectly matches an endogenous target mRNA selectively degrades the mRNA and suppresses gene expression in mammalian tissue culture cells. A single base mismatch with the target is believed to protect the mRNA from degradation, making this type of interference highly specific to the targeted gene. A short RNA with mismatches to a target sequence present in multiple copies in the 3'-untranslated region of an exogenously expressed gene can, however, silence it by translational repression. Here we report that a mismatched RNA, targeted to a single site in the coding sequence of an endogenous gene, can efficiently silence gene expression by repressing translation. The antisense strand of such a mismatched RNA requires a 5'-phosphate but not a 3'-hydroxyl group. G.U wobble base pairing is tolerated as a match for both RNA degradation and translation repression. Together, these findings suggest that a small inhibitory RNA duplex can suppress expression of off-target cellular proteins by RNA degradation or translation repression. Proper design of experimental small inhibitory RNAs or a search for targets of endogenous micro-RNAs must therefore take into account that these short RNAs can affect expression of cellular genes with as many as 3-4 base mismatches and additional G.U mismatches.

3' Untranslated Regions↗
PubMed2003

Pathogenesis of the vitreous cloud emanating from subretinal hemorrhage.

OBJECTIVE: To determine the cellular mechanism that allows subretinal hemorrhage to cloud the vitreous. METHODS: We simulated subretinal hemorrhage in a rabbit model by injecting autologous blood beneath the retina. At the first appearance of a cloud in the vitreous a vitrectomy was performed and using a surgical microscope, the retina was searched for breaks. After enucleation and fixation, the retina was searched for microscopic breaks using light and electron microscopy. The vitreous was then examined to determine the character of the cell population in the cloud. In a related study, we sampled and examined the vitreous for its cellular content in patients undergoing vitrectomy to clear cloudy vitreous emanating from subretinal hemorrhage. RESULTS: We found no breaks in the living retina of the animal models or the patients. Microscopic examination of serial sections of the rabbit retina revealed necrosis except for the internal limiting membrane. Fragments of the erythrocytes were seen within the damaged retina and on both sides of the internal limiting membrane. Electron microscopy suggested that the erythrocytic fragments had migrated across the internal limiting membrane. The vitreous cloud in both rabbits and patients contained only fragments of erythrocytes. CONCLUSIONS: Thick subretinal hemorrhage causes necrosis of the overlying retina. Fragments of the erythrocytes infiltrate the retina and cross an intact internal limiting membrane to cloud the vitreous. CLINICAL RELEVANCE: Rapid necrosis of the retina occurs over thick subretinal hemorrhage and indicates the need for early displacement of the hemorrhage from the macula if function is to be preserved and breakthrough prevented.

Animals↗
PubMed2003

A p53-dependent checkpoint pathway prevents rereplication.

Eukaryotic cells control the initiation of DNA replication so that origins that have fired once in S phase do not fire a second time within the same cell cycle. Failure to exert this control leads to genetic instability. Here we investigate how rereplication is prevented in normal mammalian cells and how these mechanisms might be overcome during tumor progression. Overexpression of the replication initiation factors Cdt1 and Cdc6 along with cyclin A-cdk2 promotes rereplication in human cancer cells with inactive p53 but not in cells with functional p53. A subset of origins distributed throughout the genome refire within 2-4 hr of the first cycle of replication. Induction of rereplication activates p53 through the ATM/ATR/Chk2 DNA damage checkpoint pathways. p53 inhibits rereplication through the induction of the cdk2 inhibitor p21. Therefore, a p53-dependent checkpoint pathway is activated to suppress rereplication and promote genetic stability.

Animals↗
PubMed2003

Management of vitreous haemorrhage.

Vitreous hemorrhage is one of the most common differential diagnoses for sudden painless decrease in vision. Often, it is caused by retinal vascular disorders secondary to common systemic ailments such as diabetes mellitus, systemic hypertension and haematological abnormalities. Sometimes it may be the beginning of a retinal tear and consequent retinal detachment that can be vision threatening if not operated early. This paper lays out practical guidelines for a tailored approach needed to arrive at the aetiology of vitreous haemorrhage so that appropriate, timely treatment can be planned.

Cryotherapy↗
PubMedDate not supplied

Cutting the encircling band.

PURPOSE: To report the effect of cutting the encircling band on ocular blood flow. METHODS: In an interventional case series of 27 eyes with an encircling band, the ocular pulse amplitude (OPA) was measured and pulsatile ocular blood flow (POBF) derived and compared with fellow eyes. The bands were cut in 11 eyes and the POBF measured at 1 month, 3 months, and 1 year. Changes in POBF, buckle height, and visual acuity were determined. RESULTS: The presence of the encircling band reduced the POBF to a mean of 43% (P < 0.001) of the fellow eye. Cutting the band resulted in a mean recovery to 85.6%. No retina detached after cutting, buckle height was only slightly diminished, and the visual acuity was unaffected. CONCLUSION: An encircling band diminishes the POBF. Cutting the band restores significant flow.

Adult↗