Biomedical subjects

K Sharma

Publications and source records attributed to K Sharma.

At least 55 records · Page 3Linked to original sources

PubMed1999

A null mutation in murine CD36 reveals an important role in fatty acid and lipoprotein metabolism.

A null mutation in the scavenger receptor gene CD36 was created in mice by targeted homologous recombination. These mice produced no detectable CD36 protein, were viable, and bred normally. A significant decrease in binding and uptake of oxidized low density lipoprotein was observed in peritoneal macrophages of null mice as compared with those from control mice. CD36 null animals had a significant increase in fasting levels of cholesterol, nonesterified free fatty acids, and triacylglycerol. The increase in cholesterol was mainly within the high density lipoprotein fraction, while the increase in triacylglycerol was within the very low density lipoprotein fraction. Null animals had lower fasting serum glucose levels when compared with wild type controls. Uptake of 3H-labeled oleate was significantly reduced in adipocytes from null mice. However, the decrease was limited to the low ratios of fatty acid:bovine serum albumin, suggesting that CD36 was necessary for the high affinity component of the uptake process. The data provide evidence for a functional role for CD36 in lipoprotein/fatty acid metabolism that was previously underappreciated.

Adipocytes↗

PubMed1999

Interdependent regulation of intracellular acidification and SHP-1 in apoptosis.

The G protein-coupled receptor agonist somatostatin (SST)-induces apoptosis in MCF-7 human breast cancer cells. This is associated with induction of wild-type p53, Bax, and an acidic endonuclease. We have shown recently that its cytotoxic signaling is mediated via membrane-associated SHP-1 and is dependent on decrease in intracellular pH (pHi) to 6.5. Here we investigated the relationship between intracellular acidification and SHP-1 in cytotoxic signaling. Clamping of pHi at 7.25 by the proton-ionophore nigericin abolished SST-signaled apoptosis without affecting its ability to regulate SHP-1, p53, and Bax. Apoptosis could be induced by nigericin clamping of pHi to 6.5. Such acidification-induced apoptosis was not observed at pHi <6.0 or >6.7. pHi-dependent apoptosis was associated with the translocation of SHP-1 to the membrane, enhanced in cells overexpressing SHP-1, and was abolished by its inactive mutant SHP-1C455S. Acidification caused by inhibition of Na+/H+ exchanger and H+ ATPase (pHi = 6.55 and 6.65, respectively) also triggered apoptosis. The effect of concurrent inhibition of Na+/H+ exchanger and H(+)-ATPase on pHi and apoptosis was comparable with that of SST. Acidification-induced, SHP-1-dependent apoptosis occurred in breast cancer cell lines in which SST was cytotoxic (MCF-7 and T47D) or not (MDA-MB-231). We conclude that: (a) SST-induced SHP-1-dependent acidification occurs subsequent to or independent of the induction of p53 and Bax; (b) SST-induced intracellular acidification may arise due to inhibition of Na+/H+ exchanger and H(+)-ATPase; and (c) SHP-1 is necessary not only for agonist-induced acidification but also for the execution of acidification-dependent apoptosis. We suggest that combined targeting of SHP-1 and intracellular acidification may lead to a novel strategy of anticancer therapy bypassing the need for receptor-mediated signaling.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed1999

Comparison of motor conduction abnormalities in lumbosacral radiculopathy and axonal polyneuropathy.

We compared the frequencies and types of motor conduction abnormalities found in peroneal and tibial nerves of patients with either L5/S1 radiculopathies (n = 47) or axonal polyneuropathies (n = 49). In axonal neuropathies, compound muscle action potentials (CMAPs) were more likely to be either unobtainable or, if present, of low amplitude, prolonged in distal latency or both. F responses were more often absent, impersistent, or prolonged in minimal latency. In contrast, CMAPs in lumbosacral radiculopathies were more likely to be normal in both amplitude and distal latency. The most frequent F-response abnormality in radiculopathies was a prolonged maximum-minimum latency range rather than abnormalities of minimal latency or persistence. Logistic regression analysis demonstrated that different patterns of motor conduction abnormalities result from lumbosacral radiculopathy and distal axonopathies. The model was able to correctly classify disease state in 76% of subjects with a sensitivity of 74% and specificity of 80%.

Adult↗

PubMed1999

Captopril-induced reduction of serum levels of transforming growth factor-beta1 correlates with long-term renoprotection in insulin-dependent diabetic patients.

The renoprotective effect of captopril on progression of diabetic nephropathy was demonstrated by the Collaborative Study Group Captopril Trial and might be independent of blood pressure. Because angiotensin II is known to stimulate the prosclerotic cytokine, transforming growth factor-beta (TGF-beta), we postulated that the renoprotective effect may be due to inhibition of TGF-beta1 production. TGF-beta1 levels were measured in serum at baseline and 6 months from patients in the captopril trial. TGF-beta1 analyses were performed on all available patient sera. Analysis was performed between the percent change in TGF-beta1 levels during the first 6 months versus the percent change in glomerular filtration rate (GFR) in the subsequent 2 years. TGF-beta1 levels increased by 11% (P = 0. 003) in the placebo group (n = 24), whereas there was a decrease of 14% (P = 0.01) in the captopril group (n = 34). There was an inverse correlation between the percent change in TGF-beta1 levels during the first 6 months and the percent change in GFR over the ensuing 2-year period in patients from both the placebo (r = -0.55, P = 0. 005) and captopril groups (r = -0.45, P = 0.008). In patients with initial GFR below 75 mL/min, there was an even stronger correlation in percent change in TGF-beta1 levels and percent change in GFR in both placebo (n = 9, r = -0.69, P = 0.03) and captopril groups (n = 21, r = -0.73, P = 0.0001). Our data suggest that captopril decreases TGF-beta1 levels in diabetic nephropathy and that changes in TGF-beta1 levels may predict the course of diabetic nephropathy.

Adult↗

PubMed1999

Active suppression of interneuron programs within developing motor neurons revealed by analysis of homeodomain factor HB9.

Sonic hedgehog (Shh) specifies the identity of both motor neurons (MNs) and interneurons with morphogen-like activity. Here, we present evidence that the homeodomain factor HB9 is critical for distinguishing MN and interneuron identity in the mouse. Presumptive MN progenitors and postmitotic MNs express HB9, whereas interneurons never express this factor. This pattern resembles a composite of the avian homologs MNR2 and HB9. In mice lacking Hb9, the genetic profile of MNs is significantly altered, particularly by upregulation of Chx10, a gene normally restricted to a class of ventral interneurons. This aberrant gene expression is accompanied by topological disorganization of motor columns, loss of the phrenic and abducens nerves, and intercostal nerve pathfinding defects. Thus, MNs actively suppress interneuron genetic programs to establish their identity.

Animals↗

PubMed1999

The 5' end of the 18S rRNA can be positioned from within the mature rRNA.

In yeast, the 5' end of the mature 18S rRNA is generated by endonucleolytic cleavage at site A1, the position of which is specified by two distinct signals. An evolutionarily conserved sequence immediately upstream of the cleavage site has previously been shown to constitute one of these signals. We report here that a conserved stem-loop structure within the 5' region of the 18S rRNA is recognized as a second positioning signal. Mutations predicted to either extend or destabilize the stem inhibited the normal positioning of site A1 from within the 18S rRNA sequence, as did substitution of the loop nucleotides. In addition, these mutations destabilized the mature 18S rRNA, indicating that recognition of the stem-loop structure is also required for 18S rRNA stability. Several mutations tested reduced the efficiency of pre-rRNA cleavage at site A1. There was, however, a poor correlation between the effects of the different mutations on the efficiency of cleavage and on the choice of cleavage site, indicating that these involve recognition of the stem-loop region by distinct factors. In contrast, the cleavages at sites A1 and A2 are coupled and the positioning signals appear to be similar, suggesting that both cleavages may be carried out by the same endonuclease.

Blotting, Northern↗

PubMed1999

The yins and yangs of ceramide.

Since their discovery over 100 years ago, sphingolipids have caught the eyes and the imagination of scientists. Modern science has made many new insights on the cell biology and day-to-day functions of many integral sphingolipids, especially those of ceramide. Ceramide is recognized as a vital second messenger in the signal transduction process mediated by receptors of many cytokines and growth factors. A great part of our current understanding of ceramide has been achieved from apoptosis-related studies, however recent data in the fields of immunology, endocrinology and neurobiology, also suggest a fundamental involvement of ceramide in the onset of diseases. Therefore, understanding the biology of ceramide could be a key to unraveling many biological mechanisms and provide information for the treatment of some common diseases.

Animals↗

PubMed1999

Association of IgA nephropathy with Clostridium difficile colitis.

Immunoglobulin A (IgA) nephropathy, the most common cause of glomerulonephritis worldwide, is usually idiopathic in origin and renal limited. Secondary IgA nephropathy has been associated with systemic disease, including such gastrointestinal tract disturbances as celiac sprue and inflammatory bowel disease. We describe gross hematuria and reversible acute renal failure from IgA nephropathy in a patient with cephalosporin-induced Clostridium difficile colitis. In addition to mesangial IgA and C3 deposition, renal histological examination showed glomerular bleeding, intratubular red blood cell casts, and acute tubular necrosis. To the best of our knowledge, this is the first report of an association between IgA nephropathy and C difficile colitis.

Acute Kidney Injury↗

PubMed1999

Base pairing between U3 small nucleolar RNA and the 5' end of 18S rRNA is required for pre-rRNA processing.

The loop of a stem structure close to the 5' end of the 18S rRNA is complementary to the box A region of the U3 small nucleolar RNA (snoRNA). Substitution of the 18S loop nucleotides inhibited pre-rRNA cleavage at site A(1), the 5' end of the 18S rRNA, and at site A(2), located 1.9 kb away in internal transcribed spacer 1. This inhibition was largely suppressed by a compensatory mutation in U3, demonstrating functional base pairing. The U3-pre-rRNA base pairing is incompatible with the structure that forms in the mature 18S rRNA and may prevent premature folding of the pre-rRNA. In the Escherichia coli pre-rRNA the homologous region of the 16S rRNA is also sequestered, in that case by base pairing to the 5' external transcribed spacer (5' ETS). Cleavage at site A(0) in the yeast 5' ETS strictly requires base pairing between U3 and a sequence within the 5' ETS. In contrast, the U3-18S interaction is not required for A(0) cleavage. U3 therefore carries out at least two functionally distinct base pair interactions with the pre-rRNA. The nucleotide at the site of A(1) cleavage was shown to be specified by two distinct signals; one of these is the stem-loop structure within the 18S rRNA. However, in contrast to the efficiency of cleavage, the position of A(1) cleavage is not dependent on the U3-loop interaction. We conclude that the 18S stem-loop structure is recognized at least twice during pre-rRNA processing.

Base Pairing↗

PubMed1999

Renal type I inositol 1,4,5-trisphosphate receptor is reduced in streptozotocin-induced diabetic rats and mice.

The mechanisms underlying glomerular hypertrophy and hyperfiltration in diabetes remain unclear. We have previously demonstrated that the cytokine transforming growth factor-beta1 (TGF-beta1) is increased in early diabetic kidney disease and TGF-beta1 inhibits the expression of the inositol 1,4,5-trisphosphate (IP3)-gated calcium channel, the type I IP3 receptor (IP3R), in mesangial cells. To test the hypothesis that reduced type I IP3R may be important in diabetic kidney disease, we evaluated type I IP3R expression in the kidney of streptozotocin-induced diabetic rats and mice. Two-week-old diabetic rats have decreased renal type I IP3R protein and mRNA levels. Immunostaining of normal rat kidney demonstrated presence of type I IP3R in glomerular and vascular smooth muscle cells, whereas diabetic rats had reduced staining in both compartments. Reduction of type I IP3R also occurred in parallel with renal hypertrophy, increased creatinine clearance, and increased renal TGF-beta1 expression in the diabetic rats. Two-week-old diabetic mice also had reduced renal type I IP3R protein and mRNA expression in association with renal hypertrophy and increased TGF-beta1 mRNA expression. These findings demonstrate that there is reduced type I IP3R in glomerular and vascular smooth muscle cells in the diabetic kidney, which may contribute to the altered renal vasoregulation and renal hypertrophy of diabetes.

Animals↗

PubMed1999

Comparison of hallway and treadmill six-minute walk tests.

The 6-min walk test (SMWT) performed in the hallway (HW) is used as a clinical indicator of functional capacity in patients with lung disease. A 6-min walk test utilizing a treadmill (TM) is easier to perform and allows easier patient monitoring. Therefore, we formulated a standardized TM SMWT protocol and compared the results with those of a HW SMWT. All patients were enrolled in a pulmonary rehabilitation program. Patients with current infection, recent change in inhaled medications or oral steroid use, and significant cardiovascular disease were excluded. Each subject performed three HW SMWTs and three TM SMWTs assigned randomly on subsequent days. There was a 30-min rest between each walk and at least a 48-h rest between each test day. All patients completed both HW and TM SMWT within 7 d. Supplemental oxygen was utilized or increased if the saturation fell below 88%. The best of the three tests was used for data analysis. Twenty-one subjects completed the protocol. The mean age was 65 +/- 10.9 yr (range, 35 to 79 yr). Ten subjects were receiving supplemental oxygen. The mean FEV(1) was 1.07 +/- 0.53 L. The mean HW SMWT distance was 1,228 +/- 255 ft (range, 612 to 1,679 ft) and the mean TM SMWT distance was 1,060 +/- 389 ft (range, 475 to 1,819 ft), which were statistically different (p = 0.01). The mean difference was 168 +/- 280 ft (range, -326 to 743 ft). Oxygen saturation and supplemental oxygen requirements did not differ significantly. The intra-test variability of the three HW SMWTs was similar to the three TM SMWTs and no significant difference in the coefficient of variation was found. A standardized TM SMWT is feasible and allows easier patient monitoring, but there is a statistically significant difference between the HW and TM SMWT distance and therefore they are not interchangeable. However, the intratest reproducibility of the TM and HW SMWTs are similar when three walks are performed in a single test session. The role of the TM SMWT in pulmonary rehabilitation requires further exploration.

Adult↗

PubMed1999

C-terminal region of human somatostatin receptor 5 is required for induction of Rb and G1 cell cycle arrest.

Ligand-activated somatostatin receptors (SSTRs) initiate cytotoxic or cytostatic antiproliferative signals. We have previously shown that cytotoxicity leading to apoptosis was signaled solely via human (h) SSTR subtype 3, whereas the other four hSSTR subtypes initiated a cytostatic response that led to growth inhibition. In the present study we characterized the antiproliferative signaling mediated by hSSTR subtypes 1, 2, 4, and 5 in CHO-K1 cells. We report here that cytostatic signaling via these subtypes results in induction of the retinoblastoma protein Rb and G1 cell cycle arrest. Immunoblot analysis revealed an increase in hypophosphorylated form of Rb in agonist-treated cells. The relative efficacy of these receptors to initiate cytostatic signaling was hSSTR5 > hSSTR2 > hSSTR4 approximately = hSSTR1. Cytostatic signaling via hSSTR5 also induced a marginal increase in cyclin-dependent kinase inhibitor p21. hSSTR5-initiated cytostatic signaling was G protein dependent and protein tyrosine phosphatase (PTP) mediated. Octreotide treatment induced a translocation of cytosolic PTP to the membrane, whereas it did not stimulate PTP activity when added directly to the cell membranes. C-tail truncation mutants of hSSTR5 displayed progressive loss of antiproliferative signaling proportional to the length of deletion, as reflected by the marked decrease in the effects of octreotide on membrane translocation of cytosolic PTP, and induction of Rb and G1 arrest. These data demonstrate that the C-terminal domain of hSSTR5 is required for cytostatic signaling that is PTP dependent and leads to induction of hypophosphorylated Rb and G1 arrest.

Animals↗

PubMed1999

Peduncular hallucinosis: an unusual sequel to surgical intervention in the suprasellar region.

Peduncular hallucinations are formed visual images often associated with sleep disturbance, and are caused by lesions in the midbrain, pons and diencephalon. In the present study, we report two patients who developed peduncular hallucinations following surgery in the suprasellar region. In one of these, the peduncular hallucinations were a sequel to endoscopic third ventriculostomy, while in the other, they were due to diencephalon and mid-brain compression by a postoperative clot following excision of a hypothalamic astrocytoma.

Astrocytoma↗

PubMed1999

Inoculation injuries in hospitals in Trinidad and Tobago.

This paper reviews the frequency of inoculation injuries, which occurred in hospitals in Trinidad and Tobago from 1991 to 1997, inclusive. A total of 397 cases of inoculation injuries were detected. Significantly more of these injuries occurred during diagnostic or therapeutic procedures (231, or 58.2%; G = 41.2, df 9, p < 0.001) than during disposal of needles and other sharps (136, or 34.3%), certain situations remote from patient care (21, or 5.2%), and 'rogue incidents' related to unsafe disposal with later injury to janitors or others (9, or 2.3%). No statistically significant monthly or seasonal variations occurred in the incidence of reported inoculation injuries. The two institutions that saw the largest number of patients, the Port-of-Spain General and San Fernando General Hospitals, accounted for the largest number of cases of inoculation injury, with 139 (35.0%) and 135 (34.0%), respectively. Interestingly enough, there were 42 reported inoculation incidents at the St. Ann's Hospital for the Mentally Impaired and 23 (52.5%) of these were bites, most of them occurring during attempted procedures. Nurses were the main recipients of inoculation injuries (287 cases, or > 72%), followed by doctors (9.3%), and ward maids (6.2%). The main modes of inoculation were needle sticks (305, or 76.8%). Bites (34, 8.6%), injuries with sharps other than needles (29, or 7.3%), and splashes (29, or 7.3%) were the other types seen. One recipient was found to be infected with HIV following accidental inoculation. The infection control methodologies used in hospitals in Trinidad and Tobago are reviewed and recommendations for preventing injuries are outlined.

Accidents, Occupational↗

PubMed1998

LIM homeodomain factors Lhx3 and Lhx4 assign subtype identities for motor neurons.

The circuits that control movement are comprised of discrete subtypes of motor neurons. How motor neuron subclasses develop and extend axons to their correct targets is still poorly understood. We show that LIM homeodomain factors Lhx3 and Lhx4 are expressed transiently in motor neurons whose axons emerge ventrally from the neural tube (v-MN). Motor neurons develop in embryos deficient in both Lhx3 and Lhx4, but v-MN cells switch their subclass identity to become motor neurons that extend axons dorsally from the neural tube (d-MN). Conversely, the misexpression of Lhx3 in dorsal-exiting motor neurons is sufficient to reorient their axonal projections ventrally. Thus, Lhx3 and Lhx4 act in a binary fashion during a brief period in development to specify the trajectory of motor axons from the neural tube.

Animals↗

PubMed1998

Induction of wild-type p53, Bax, and acidic endonuclease during somatostatin-signaled apoptosis in MCF-7 human breast cancer cells.

Somatostatin (SST) analogs inhibit tumor cell growth by exerting direct anti-proliferative effects with cytostatic (growth arrest) or cytotoxic (apoptosis) consequences. The SST analog SMS 201-995 (octreotide, OCT) inhibits growth of MCF-7 human breast adenocarcinoma cells, which express multiple SSTRs. Its action has been reported to result in either apoptosis or growth arrest, but the underlying mechanisms have not been elucidated in this tumor cell model. Here, we report that OCT elicits cytotoxic response in these cells, leading to apoptosis, which is associated with a rapid, time-dependent induction of wild-type p53 and an increase in Bax. There was no G1 cell-cycle arrest in these cells during OCT treatment as suggested by the decrease in G1/S ratio and the lack of induction of pRb and p21. Additionally, we demonstrate that OCT-induced DNA fragmentation in this cell line is due to selective activation of a cation-insensitive acidic endonuclease. Our data provide a rationale for utilizing SST analogs to treat SSTR-positive breast cancer cells expressing wild-type p53.

Adenocarcinoma↗

PubMed1998

Transforming growth factor-beta1 stimulates protein kinase A in mesangial cells.

We recently demonstrated that transforming growth factor-beta (TGF-beta) stimulates phosphorylation of the type I inositol 1,4, 5-trisphosphate receptor (Sharma, K., Wang, L., Zhu, Y., Bokkala, S., and Joseph, S. (1997) J. Biol. Chem. 272, 14617-14623), possibly via protein kinase A (PKA) activation in murine mesangial cells. In the present study, we evaluated whether TGF-beta stimulates PKA activation. Utilizing a specific PKA kinase assay, we found that TGF-beta increases PKA activity by 3-fold within 15 min of TGF-beta1 treatment, and the enhanced kinase activity was completely reversed by the inhibitory peptide for PKA (PKI; 1 microM). In mesangial cells transfected with a PKI expression vector, enhanced PKA activity could not be demonstrated with TGF-beta1 treatment. TGF-beta1 was also found to stimulate translocation of the alpha-catalytic subunit of PKA to the nucleus by Western analysis of nuclear protein as well as by confocal microscopy. TGF-beta1-mediated phosphorylation of cAMP response element-binding protein was completely reversed by H-89 (3 microM), a specific inhibitor of PKA. Stimulation of fibronectin mRNA by TGF-beta1 was also attenuated in cells overexpressing PKI. We thus conclude that TGF-beta stimulates the PKA signaling pathway in mesangial cells and that PKA activation contributes to TGF-beta stimulation of cAMP response element-binding protein phosphorylation and fibronectin expression.

Animals↗

PubMed1998

G protein coupled receptor signaled apoptosis is associated with activation of a cation insensitive acidic endonuclease and intracellular acidification.

Apoptosis associated oligonucleosomal fragmentation of DNA can result from the activation of endonucleases that exhibit different pH optima and are either sensitive or insensitive to divalent cations. DNA fragmentation due to activation of cation sensitive endonucleases occurs in the absence of a change in intracellular pH whereas intracellular acidification is a feature of apoptosis characterized by activation of cation insensitive acidic endonuclease. We have reported earlier that somatostatin (SST) induced DNA fragmentation and apoptosis is signaled in a receptor subtype selective manner uniquely via human somatostatin receptor subtype 3 (hSSTR3). In the present study we investigated the pH dependence and cation sensitivity of endonuclease induced in hSSTR3 expressing CHO-K1 cells by the SST agonist octreotide (OCT) and its effect on intracellular pH. We show that OCT induced apoptosis is associated with selective stimulation of a divalent cation insensitive acidic endonuclease. The intracellular pH of of cells undergoing OCT induced apoptosis was 0.9 pH units lower than that of control cells. The effect of OCT on endonuclease and pH was inhibited by orthovanadate as well as by pretreatment with pertussis toxin, suggesting that hSSTR3 initiated cytotoxic signaling is protein tyrosine phosphatase mediated and is G protein dependent. These findings suggest that intracellular acidification and activation of acidic endonuclease mediate wild type p53 associated apoptosis signaled by hormones acting via G protein coupled receptors.

Acids↗