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Biomedical subjects

L M Kaplan

Publications and source records attributed to L M Kaplan.

At least 19 recordsLinked to original sources
PubMed2005

Changes in serum ghrelin predict weight loss after Roux-en-Y gastric bypass in rats.

BACKGROUND: Although Roux-en-Y gastric bypass (RYGB) is an effective and widely used therapy for severe obesity, the mechanisms by which it induces weight loss are not well understood. Several studies have shown that RYGB in human patients causes a decrease in circulating levels of ghrelin, a gastric hormone that strongly stimulates food intake. Substantial variation in the effect of RYGB on serum ghrelin has been reported in different studies and among individual patients, suggesting that regulation of this hormone is complex and subject to genetic and other patient-specific factors. To control for these factors and to enable more detailed study of physiologic mechanisms, we have recently developed a clinically relevant rat model of RYGB. In this study, we used this model to examine the effect of RYGB on serum ghrelin levels. METHODS: Fifteen Sprague-Dawley rats that had received a high-fat diet to induce moderate obesity underwent RYGB. The operation closely resembled the procedure in humans. Serum samples were collected 1 month before and 3 months after RYGB, and serum ghrelin levels were measured. The primary outcomes of the study were the changes in body weight, food intake, and circulating ghrelin levels after RYGB. A multiple linear regression model was developed to examine the relationship between ghrelin levels and weight change after RYGB. RESULTS: Three months after the procedure, RYGB-treated rats weighed 20 +/- 5% less than they would have, had they not undergone the procedure. Despite the weight loss, serum ghrelin levels were 38 +/- 6% lower than before surgery. There was appreciable variation in the weight loss in individual animals, and preoperative weight and pre- and postoperative ghrelin levels were the best predictors of postoperative weight loss. Thus, the animals who had the greatest weight loss were those that were heaviest before surgery. These rats had the highest preoperative and lowest postoperative ghrelin levels. CONCLUSIONS: Using our recently developed rat model of RYGB, we found that postoperative weight loss is correlated with the magnitude of the decrease in circulating ghrelin levels. This correlation provides the strongest evidence to date that altered ghrelin signaling contributes to weight loss after this operation. The lower level of circulating ghrelin after RYGB likely blunts the appetitive drive, leading to decreased food intake in these animals.

Animals↗
PubMed1999

Heterogeneous nuclear ribonucleoprotein I (hnRNP-I/PTB) selectively binds the conserved 3' terminus of hepatitis C viral RNA.

Hepatitis C virus (HCV) is a positive-strand RNA virus whose genome is replicated by a direct RNA-to-RNA mechanism. Initiation of negative-strand RNA synthesis is believed to proceed from the 3' end of the genomic RNA. The high conservation of the 3' terminus suggests that this region directs the assembly of proteins required for the initiation of RNA replication. We sought to determine whether host proteins bind specifically to this RNA structure. We observed specific binding of cellular proteins to labeled 3'-terminal RNA by mobility shift analysis. UV crosslinking revealed that the predominant 3'-terminal RNA-binding protein migrates as a single, 60-kDa species that can be precipitated by monoclonal antibodies directed against heterogeneous nuclear ribonucleoprotein I, also called polypyrimidine tract-binding protein (hnRNP-I/PTB), a protein previously shown to bind to the 5' internal ribosome entry site (IRES) of the HCV genome. Purified hnRNP-I/PTB also bound selectively to the 3' end of the HCV genome. hnRNP-I/PTB binding requires the upstream two stem-loop structures (SL2 and SL3) but not the most 3'-terminal stem-loop (SL1). Minor alteration of either the stem or loop sequences in SL2 or SL3 severely compromised hnRNP-I/PTB binding, suggesting extremely tight RNA structural requirements for interaction with this protein. hnRNP-I/PTB does not bind to either end of the antigenomic RNA strand and binds to the 5' IRES element of the genome at least 10-fold less avidly than to the 3' terminus. The strong, selective, and preferential binding of hnRNP-I/PTB to the 3' end of the HCV genome suggests that it may be recruited to participate in viral replication, helping to direct initiation of negative-strand RNA synthesis, stabilize the viral genome, and/or regulate encapsidation of genomic RNA.

Animals↗
PubMed1999

Mutations in the NS5A region do not predict interferon-responsiveness in american patients infected with genotype 1b hepatitis C virus.

A striking association has been demonstrated recently between mutations in amino acid residues 2209-2248 of the nonstructural protein 5a (NS5a) region of hepatitis C virus (HCV) and sustained responses to interferon in Japanese patients infected with genotype 1b. Therefore, analysis of this sequence has been suggested as a predictor of treatment response. We sought to determine whether mutations in this region predict outcome in U.S. patients infected with genotype 1b hepatitis C virus (HCV-1b). We analyzed stored pretreatment sera retrospectively from 22 patients with HCV-1b infection who had received interferon alpha-2b (IFNalpha-2b) as part of a controlled trial. Two patients were sustained responders (SR), 7 were transient responders (TR), and 13 were nonresponders (NR). We performed nested reverse transcription-polymerase chain reaction (RT-PCR) on extracted RNA using primers flanking HCV amino acids 2209-2248 and sequenced the PCR products directly. The deduced amino acid sequences were compared with the prototype HCV-J. Isolates with four or more deviations from the prototype were defined as "mutant" type, those with one to three substitutions as "intermediate" type, and those matching the prototype as "wildtype." Of the 22 HCV-1b isolates, 6 were wildtype, 11 intermediate type, and 5 mutant type. Both of the SRs were intermediate type. The 20 TRs and NRs were distributed among mutant (5), intermediate (9), and wildtype (6). Of the five patients with mutant virus, four were NR and one a TR. Variation in NS5a(2209-2248) fails to predict interferon responsiveness in this cohort of American patients infected with HCV-1b. Thus, the utility of this sequence as a predictor of interferon responsiveness appears to be specific to Japanese patients and may reflect differences between patient groups in treatment regimens, host genetic background, or alterations in the interferon signaling pathway induced by surrounding sequences within or outside NS5a. Overall, NS5a is not as integral a determinant of interferon responsiveness as previously suggested.

Amino Acid Sequence↗
PubMed1998

Increase in plasma leptin and Lep mRNA concentrations by food intake is dependent on insulin.

Obese (Lep) gene expression and leptin secretion are regulated by changes in food intake. However, the mechanism by which leptin concentrations are altered by fasting and feeding is unclear. Since these changes occur in parallel with changes in plasma insulin, it is possible that the changes observed are mediated by insulin. To test this hypothesis, we studied the role of insulin in the regulation of Lep gene expression in epididymal fat and leptin secretion during feeding. As shown previously, fasted animals showed significant reductions in Lep mRNA, plasma leptin, and plasma insulin concentrations. Conversely, feeding increased plasma insulin, Lep mRNA, and plasma leptin. In streptozotocin (STZ)-treated animals, plasma insulin concentrations were low. This was associated with low Lep mRNA and plasma leptin concentrations. Changes in food intake, whether fasting or feeding, did not significantly alter plasma insulin levels in STZ-treated animals. Under these circumstances, Lep mRNA and plasma leptin concentrations also remained low. Our results demonstrate that the decrease in Lep mRNA and plasma leptin during fasting and the increase with feeding are dependent on changes in the plasma insulin concentration.

Animal Feed↗
PubMed1998

Analysis of impaired exercise capacity in patients with cirrhosis.

Exercise limitation in cirrhosis is typically attributed to a cirrhotic myopathy (without impaired oxygen utilization) and/or a cardiac chronotropic dysfunction. We performed symptom-limited cardiopulmonary exercise testing in 19 cirrhotics without confounding variables (cardiopulmonary disease, beta blockade, anemia, smoking). Twelve concurrently exercised patients without cirrhosis and with normal resting pulmonary function were controls. Oxygen consumption (VO2) at peak exercise, at anaerobic threshold (VO2-AT), work rate (WR), and heart rate (HR) were measured. Cirrhotics had significantly lower peak WR (73+/-4 vs 107+/-7% predicted, p < 0.001), VO2 (72+/-4 vs 98+/-5% predicted, P < 0.001), VO2-AT (53+/-4 vs 71+/-5% predicted peak VO2, P < 0.01), HR (83+/-2 vs 91+/-2% predicted, P < 0.01) and were more likely to have chronotropic dysfunction (peak HR < 85% predicted). Six cirrhotics had normal aerobic capacity (peak VO2 > 80% predicted), while 13 were abnormal. The abnormals had an earlier AT (46+/-2 vs 67+/-3% predicted peak VO2, P < 0.05) but no difference in peak HR percent predicted was found. In conclusion, two thirds of cirrhotics, without confounding factors, have significantly reduced aerobic capacity. Cirrhotic myopathy (without impaired O2 utilization) and cardiac chronotropic dysfunction do not adequately account for the observed decrease in aerobic capacity.

Adult↗
PubMed1998

Serum leptin in children and young adults with inflammatory bowel disease.

BACKGROUND: Pediatric inflammatory bowel disease is often associated with growth failure and inadequate energy intake. Although several circulating cytokines are known to be elevated in inflammatory bowel disease, the mechanism for the related anorexia has not been described. Leptin is a newly recognized circulating protein that is an important regulator of appetite and energy metabolism; leptin levels are elevated in several animal models of inflammation. This study was conducted to determine whether serum leptin levels are elevated in young patients with inflammatory bowel disease. METHODS: One hundred twelve children and young adults with Crohn's disease or ulcerative colitis were studied prospectively. Forty-two patients with other gastrointestinal illnesses were used as control subjects. Height, weight, erythrocyte sedimentation rate, serum albumin concentration, and clinical information were collected prospectively, and leptin was measured by radioimmunoassay of stored serum. RESULTS: No significant differences in leptin levels were found among disease groups or control subjects. Body mass index and gender were the only independent predictors of serum leptin in all groups examined. Disease activity varied inversely with serum leptin in patients with Crohn's disease, but these differences were explained entirely by variations in body mass index. CONCLUSIONS: The determinants of serum leptin were the same in young patients with inflammatory bowel disease as in normal populations, indicating that alterations in leptin levels are unlikely to mediate the anorexia and growth failure associated with this disease.

Adolescent↗
PubMed1998

Response to symptom-limited exercise in patients with the hepatopulmonary syndrome.

OBJECTIVE: To study the response to symptom-limited exercise in patients with the hepatopulmonary syndrome (HPS). DESIGN: The response to maximal cardiopulmonary exercise (CPX) was studied in 5 patients with HPS and compared with 10 case control (normoxemic, NC) cirrhotics (matched for age, gender, etiology and severity of liver disease, tobacco use, and beta-blocker therapy) and 9 hypoxemic control cirrhotics (HC) without clinical evidence of HPS. SETTING: Cardiopulmonary exercise physiology laboratory in a tertiary care referral center. PATIENTS: Cirrhotics referred for CPX as part of their preliver transplantation evaluation. MEASUREMENTS: Standard pulmonary function tests and echocardiography were performed to assess resting pulmonary and cardiac function. Peak oxygen consumption (VO2), minute ventilation, arterial blood gases, and dead space (VD/VT) were determined during symptom-limited maximal CPX. RESULTS: Resting spirometry and lung volumes were similar between HPS and NC subjects, while HC subjects had restrictive physiology. Differences existed in diffusing capacity corrected for hemoglobin and alveolar volume percent predicted (HPS, 45+/-2 vs NC, 68+/-3, p<0.05; vs HC, 70+/-4, p<0.05), PaO2 (HPS, 70+/-5 mm Hg; HC, 79+/-3 mm Hg, vs NC, 102+/-3 mm Hg, p<0.05) and alveolar-arterial (A-a) O2 gradient (HPS, 42+/-8 mm Hg vs HC, 27+/-2 mm Hg, p<0.05; vs NC, 6+/-2 mm Hg, p<0.05). During CPX, HPS patients achieved a lower peak VO2 percent predicted (HPS, 55+/-6 vs NC, 73+/-3, p<0.05; vs HC, 71+/-5, p<0.05) and VO2 at the ventilatory threshold as percent predicted peak VO2 (HPS, 36+/-2 vs NC, 55+/-4, p<0.05; vs HC 55+/-5, p<0.05). While no differences existed in heart rate and breathing reserve, HPS patients had significantly lower PaO2 (HPS, 50+/-5 mm Hg vs NC, 97+/-4 mm Hg, p<0.05; vs HC, 87+/-6 mm Hg, p<0.05), wider A-a O2 gradient (HPS, 73+/-5 mm Hg vs NC, 13+/-3 mm Hg, p<0.05; vs HC, 31+/-5 mm Hg, p<0.05) and higher VD/VT (HPS, 0.36+/-.03 vs NC, 0.18+/-.02, p<0.05; vs HC, 0.28+/-.02, p<0.05) at peak exercise. For HPS patients, VO2 was negatively correlated with VD/VT (r2=0.9) and positively correlated with PaO2 (r2=0.41) at peak exercise. CONCLUSIONS: Patients with HPS demonstrate a severe reduction in aerobic capacity, beyond that found in cirrhotics without syndrome. The significant hypoxemia and elevated VD/VT at peak exercise suggest that an abnormal pulmonary circulation contributes to further exercise limitation in patients with HPS.

Adult↗
PubMed1998

Regulation of leptin expression and secretion by corticosteroids and insulin. Implications for body weight.

Leptin is an important hormone that has potent effects on appetite and body weight. The regulation of leptin gene expression and secretion by corticosteroids and insulin was studied in the rat. Adrenalectomy resulted in a significant reduction in leptin gene expression and secretion. The reduction was corrected by hormonal replacement with corticosterone pellets, showing that normal levels of circulating corticosteroids are required to maintain leptin expression and secretion in the body. Chronic treatment with dexamethasone (DEX) over 3 wk did not significantly increase leptin gene expression and secretion, contrary to earlier reports using shorter treatment paradigms. The profound weight loss associated with chronic DEX treatment may have abrogated the direct stimulatory effect of DEX on leptin gene expression and secretion, indicating a possible crosstalk between corticosteroids and leptin in the regulation of body weight. Shorter-term treatment of animals with DEX (3.7 micrograms/g body wt; 24 h) increased leptin gene expression and secretion about 2-fold and 1.4-fold, respectively. The increase was independent of circulating insulin concentrations. In streptozotocin-treated rats, short-term DEX treatment increased leptin gene expression and secretion about 3.5-fold and 2-fold, respectively. The data indicate that circulating leptin concentrations and adipose tissue leptin expression are dependent on corticosteroids and insulin. Although acute DEX treatment resulted in a stimulatory effect on leptin secretion and expression, chronic DEX treatment did not. The stimulatory effect of DEX on leptin is independent of circulating insulin concentrations.

Adipose Tissue↗
PubMed1997

Regulation of anterior pituitary galanin gene expression by thyroid hormone.

Thyroid hormone is required for basal and estrogen-induced expression of anterior pituitary galanin. Steady-state anterior pituitary galanin mRNA levels decreased 6-fold in hypothyroid rats after 3 weeks of treatment. Similarly, hypothyroidism resulted in a 2.6-fold decrease in estrogen induction of galanin gene expression. The effect of thyroid hormone on anterior pituitary galanin gene expression appears to be exerted, at least in part, at the pituitary itself. Transient expression assays in GH3 cells suggest the involvement of transcriptional mechanisms in the regulation of galanin gene expression by thyroid hormone. A region between -41 and -132 bp upstream of the transcriptional start site confers thyroid hormone responsiveness to the galanin gene. Gel-mobility shift assays show specific binding of 'SPI-like' proteins in GH3 nuclear extracts to this region of the galanin gene. This binding was greatly enhanced by thyroid hormone.

Animals↗
PubMed1995

Effectiveness of current technology in the diagnosis and management of lower gastrointestinal hemorrhage.

Lower gastrointestinal hemorrhage is a common clinical problem for which multiple diagnostic tests and therapeutic interventions have been developed but no optimal approach has been established. We reviewed 107 consecutive patients admitted to the Massachusetts General Hospital for management of acute lower gastrointestinal hemorrhage to determine the effectiveness of diagnostic and management technologies, with particular attention to urgent colonoscopy. Colonoscopy yielded a diagnosis in 90% of patients, provided the opportunity for successful therapy in 9 of 13 patients (69%), and shortened hospital stay. Angiography performed after a scan positive for bleeding was often diagnostic, and angiography provided the means for successful therapy in 5 of 10 patients (50%). Barium enema and sigmoidoscopy had lower clinical yields. Although roles exist for other technologies, colonoscopy is the most convenient and effective first test in the evaluation of patients with significant lower gastrointestinal hemorrhage. Diagnostic yield, therapeutic opportunity, and cost effectiveness are maximized in early studies.

Acute Disease↗
PubMed1995

Clinical, echocardiographic, and hemodynamic evidence of cardiac tamponade caused by large pleural effusions.

Large pleural effusions are typically associated with dyspnea and potential respiratory compromise. Experimental evidence suggests that with large effusions, increased intrapleural pressure may be transmitted to the pericardial space, resulting in impaired cardiac filling and reduced stroke volume. We report two cases in which large pleural collections were complicated by hypotension. The effusions were due to an infected right hepatic hydrothorax (Case 1) and a left malignant effusion (Case 2). Echocardiography demonstrated right and left ventricular diastolic collapse, respectively, confirming a diagnosis of cardiac tamponade. Large volume thoracentesis resulted in immediate hemodynamic improvement as demonstrated by a reduction in right ventricular and atrial pressures (Case 1) and echocardiographic resolution of left ventricular diastolic collapse (Case 2). These cases establish that large pleural effusions can cause hemodynamically significant cardiac tamponade. In addition, they illustrate how the demonstration of cardiac compressive physiology can significantly alter the therapeutic approach to large pleural effusions.

Adult↗
PubMed1994

Respiratory dysfunction in amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder of the voluntary motor system. Involvement of the respiratory system is inevitable and leads to the development of respiratory failure, the usual cause of death in this disorder. ALS at present is incurable, and only symptomatic treatment is available. This article presents guidelines for the recognition and management of respiratory failure.

Amyotrophic Lateral Sclerosis↗
PubMed1993

Parenterally transmitted hepatitis: viruses, vaccines, and antiviral therapy.

The introduction of safe and effective vaccines as well as the identification of antiviral therapy that eradicates virus in many infected patients augurs well for the control of HBV and, by extension, HDV infection. The key to ultimate success will be the universal availability of immunization. The recent elucidation of the hepatitis C genomic structure will eventually lead to fundamental understanding of the mechanisms underlying the life cycle of HCV, which appears to elude both natural and synthetic defensive measures. The best hope for control of this virus in the near future rests in careful screening of the blood supply and alteration of high-risk lifestyles. The next phase of antiviral and vaccine development for all of these agents will depend on recently acquired knowledge of virus-specific enzymatic processes, molecular interactions between viruses and host cells, and our ability to interfere selectively with these processes.

Antiviral Agents↗
PubMed1992

A role for hepatitis C virus infection in type II cryoglobulinemia.

BACKGROUND: Type II cryoglobulinemia is a vasculitis characterized by cryoglobulins consisting of complexes of polyclonal IgG and monoclonal IgM rheumatoid factors. The cause of these immune complexes is unknown, though both the hepatitis B (HBV) and C (HCV) viruses have been suspected. METHODS: We studied 19 patients with Type II cryoglobulinemia for markers of HCV and HBV infection. Quantitative HCV antibody and RNA studies were performed on whole serum, cryoprecipitates, and supernatants. RESULTS: Eight patients (42 percent) had HCV antibodies, and 16 (84 percent) had HCV RNA: Of the 19 patients, 5 (26 percent) had HBV markers, but only 1 had evidence of active HBV infection. Control serum samples from nine patients with Type I cryoglobulinemia were negative for HCV antibody and HCV RNA: There was a close, although not exclusive, association of one type of rheumatoid factor (WA) with HCV RNA: HCV antibody and HCV RNA were concentrated approximately 10-fold and 1000-fold, respectively, in the Type II cryoglobulins examined. CONCLUSIONS: Type II cryoglobulinemia is strongly associated with concomitant HCV infection and a high rate of false negative serologic tests. HCV virions and HCV antigen-antibody complexes are concentrated in the cryoprecipitates, most commonly in association with the WA type of rheumatoid factor, suggesting a role for HCV in the pathogenesis of mixed cryoglobulinemia.

Cryoglobulinemia↗
PubMed1991

Sexually dimorphic expression of the growth hormone-releasing hormone gene is not mediated by circulating gonadal hormones in the adult rat.

The sexual dimorphism characterizing GH secretion in the rat is thought to be related to differences in the hypothalamic synthesis and release of the GH-regulating peptides, GH-releasing hormone (GHRH), and somatostatin. Therefore, the influence of gender and sex steroid hormones on hypothalamic expression of the GHRH gene in adult rats were examined. GHRH messenger RNA (mRNA) levels were measured in individual rat hypothalami by Northern hybridization analysis using a 32P-labeled complementary DNA encoding rat GHRH. Destruction of hypothalamic GHRH neurons by neonatal treatment with monosodium glutamate caused similar 3-fold reductions in the levels of GHRH mRNA in adult male and female animals. In three separate experiments, hypothalamic GHRH mRNA concentrations in male rats were 2- to 3-fold greater than in randomly cycling females (four or five rats per group; P less than 0.01). In spite of the greater abundance of GHRH mRNA abundance in the male rat hypothalamus, circulating gonadal steroids lacked the ability to modulate GHRH gene expression in adult animals, since neither gonadectomy nor pharmacological sex steroid replacement changed GHRH mRNA levels in the hypothalamus of male and female adult rats. Furthermore, GHRH mRNA concentrations in female rats were similar during the proestrus, estrus, and diestrus phase of the estrous cycle. Also, GH inhibited hypothalamic GHRH gene expression in a sex-specific manner. Exposure to high levels of GH secreted by the MtTW15 tumor for 4 weeks reduced GHRH mRNA concentrations 7-fold in male rats (P less than 0.001) but only 2-fold in females (P less than 0.05). These studies demonstrate that GHRH gene expression in the rat hypothalamus is sexually dimorphic. Basal mRNA levels are greater in male rats, and expression in male hypothalami is more sensitive to feedback inhibition by GH than expression in females. There is no evidence for regulation of GHRH mRNA levels by either testosterone or estrogen in adult rats. These gender differences in GHRH gene expression likely contribute to the generation of a sex-specific pattern of GH secretion.

Animals↗
PubMed1991

Coexpression of galanin and adrenocorticotropic hormone in human pituitary and pituitary adenomas.

Galanin is a neuropeptide that regulates the secretion of several pituitary hormones, including prolactin (PRL) and growth hormone (GH). Galaninlike immunoreactivity (Gal-IR) and galanin mRNA in the rat anterior pituitary is cell lineage specific, with predominant expression in lactotrophs and somatotrophs. The authors examined the cellular distribution of human Gal-IR in seven normal postmortem pituitaries and 62 pituitary tumors by immunoperoxidase staining. In contrast to the rat, Gal-IR in human anterior pituitaries was present in corticotrophs scattered throughout the gland, but not in lactotrophs, somatotrophs, thyrotrophs, or gonadotrophs. Distinct Gal-IR also was present in hyperplastic and neoplastic corticotrophs in 19 of 22 patients with Cushing's disease. In noncorticotroph cell tumors, unequivocal Gal-IR was present in 5 of 11 GH-secreting tumors associated with clinical acromegaly, 9 of 18 nonfunctioning pituitary adenomas, and 2 of 14 prolactinomas. Of these galanin-positive tumors, four of the five GH-secreting adenomas, six of the nine nonfunctioning adenomas, and both of the prolactinomas also contained adrenocorticotropic hormone immunoreactivity (ACTH-IR). Immunostaining and in situ hybridization on adjacent sections using an 35S-labeled probe complementary to human galanin mRNA demonstrated predominant galanin expression in normal corticotrophs. Immunoelectron microscopy confirmed the presence of Gal-IR in pituitary cells characteristic of corticotrophs in both normal and neoplastic pituitaries. Thus, as in the rat, galanin gene expression in the human pituitary is cell-type specific. Unlike the rat, however, human galanin gene expression is restricted to the corticotroph lineage. Studies of tumors confirmed the observed coexpression of galanin and adrenocorticotropic hormone. The divergent cell type specificity of galanin production in human and rat pituitaries reflects different patterns of gene activation in these two species. In addition, these results suggest that galanin in the human pituitary may participate locally in the regulation of the hypothalamic-pituitary-adrenal axis.

Adenoma↗