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Biomedical subjects

S K Lim

Publications and source records attributed to S K Lim.

At least 37 records · Page 2Linked to original sources

Consequences of haemolysis without haptoglobin.

Haptoglobin (Hp), a conserved plasma glycoprotein, forms very stable soluble complexes with free plasma haemoglobin. Haemoglobin binding by haptoglobin is thought to be important in the rapid hepatic clearance of haemoglobin from the plasma and in the inhibition of glomerular filtration of haemoglobin. It is thought to reduce haemoglobin-induced renal damage during haemolysis. To evaluate these functions, Hp knockout (Hp-/-) mice were created. The Hp-/- mouse was generated by a standard gene replacement technique in mouse embryonic stem cells. These mice were evaluated with and without haemolysis using several parameters: mortality, haemoglobin clearance, renal tissue damage and function. Hp-/- mice were viable but had a small, significant reduction in postnatal viability. The lack of Hp did not impair clearance of free plasma haemoglobin. Induction of severe haemolysis by phenylhydrazine caused extensive haemoglobin precipitation in the renal tubular cells. However, haemoglobin precipitation in the kidney was not increased in Hp-/- mice. Nevertheless, Hp-/- mice were more susceptible to phenylhydrazine with a mortality rate of 55% in Hp-/- mice versus 18% in Hp+/+ mice. In general, phenylhydrazine-treated Hp-/- mice suffered greater tissue damage, as evidenced by the induction of a hepatic acute phase response, resulting in increased plasma alpha1-acidic glycoprotein (AGP) levels and higher plasma malonaldehyde (MDA) and 4-hydroxy-2(E)-nonenal (HNE) levels. Gross pathological analysis indicated that the kidney was the most affected tissue in phenylhydrazine-treated Hp-/- and Hp+/+ mice, and Hp-/- mice were more severely affected. They had lower mitotic indices in their kidneys, higher basal levels of renal lipid peroxidation, as evidenced by levels of malonaldehyde and 4-hydroxy-2(E)-nonenal (MDA/HNE) and elevated levels of 8-hydroxyguanine (but not other products of oxidative DNA damage). There also was increased induction of haem oxygenase-1. The more severe renal damage in Hp-/- mice was also evident in the delayed erythropoietin gene expression and poorer renal clearance of [3H]-inulin. The reduction in glomerular filtration function in Hp+/+ and Hp-/- mice could be restored to baseline by vasodilators (prazosin or diazoxide), implicating renal vasoconstriction as a major mechanism of acute renal failure during induced haemolysis. These data suggest that Hp plays a pivotal role in reducing renal oxidative damage during haemolysis.

Aldehydes↗

Haptoglobin, an inflammation-inducible plasma protein.

Sterile tissue injury or infection initiates a local inflammatory response that mobilizes a systemic acute phase reaction resulting in, among other things, the induction of genes encoding the acute phase plasma proteins (APPs). In all vertebrates, a common set of APPs is increased and exerts essential protective functions. Haptoglobin (HP), one of the major APPs, acts as a high-affinity hemoglobin-binding protein and antioxidant. Liver is the major site of HP synthesis; however, regulated, low level expression is also detected in other organs. Induction of the Hp gene is mediated by interleukin-6-type cytokines and is synergistically enhanced by glucocorticoids. Growth stimulation of hepatic cells in vivo or in vitro suppresses the Hp gene-inducing effects of inflammatory cytokines. Receptors for IL-6 cytokines mediate induction of the Hp gene by the transcription factors signal transducer and activator of transcription-3 (STAT3) and CAAT/enhancer binding protein beta (C/EBPbeta), but attenuate the stimulation through co-activated STAT5 and mitogen-activated protein kinases, ERK-1 and ERK-2. The specificity by which the related cytokines, IL-6, oncostatin M, and leukemia inhibitory factor, regulate Hp gene transcription is determined by the profile of the cytokine receptor subunits expressed on the target cells and the relative extents by which these receptors activate the intracellular signaling pathways. The current hypothesis is that HP exerts an anti-inflammatory activity and that by the degree with which HP attenuates the inflammatory process, including the production of IL-6 cytokines, it determines the level and duration of acute phase expression of the Hp gene.

Animals↗

Cerebrospinal fluid and plasma concentrations of leptin, NPY, and alpha-MSH in obese women and their relationship to negative energy balance.

Leptin and its principal mediators, NPY and alpha-MSH are postulated to play a pivotal role in energy balance. To determine the possibility of the disturbance in neuropeptides in human obesity and their consequent changes in response to negative energy balance, we evaluated plasma and cerebrospinal fluid (CSF) leptin, NPY, and alpha-MSH levels in obese women before and after weight loss in comparison with normal control women. Subjects included 16 obese women [mean body mass index (BMI), 35.6 kg/m(2)] before and after weight loss induced by a 2-wk very low caloric diet (800 kcal/d) and 14 normal weight women (mean BMI, 20.4 kg/m(2)). The CSF to plasma leptin ratio in normal weight subjects was 2.3-fold higher than that in obese subjects. After weight loss in obese subjects, plasma leptin levels decreased by 40% and CSF levels decreased by 51%. There was a positive linear correlation between CSF and plasma leptin levels at baseline in obese subjects (r = 0.74, P < 0.05) and a positive logarithmic correlation in normal weight subjects (r = 0.89, P < 0.05) and in obese subjects after weight loss (r = 0.64, P < 0.05). The BMI was negatively correlated with the CSF to plasma leptin ratio (r = -0.86, P < 0.05) in all subjects. Neither the baseline plasma levels nor the baseline CSF levels of NPY were different between normal weight subjects and obese subjects. After weight loss, the CSF NPY level decreased significantly compared with baseline values in obese subjects. The alpha-MSH levels in plasma and CSF did not differ significantly from controls in obese subjects at baseline or after weight loss. Baseline CSF leptin level correlated with neither the baseline CSF NPY level nor the baseline CSF alpha-MSH level. In conclusion, this study demonstrated that the efficiency of brain leptin delivery is reduced in human obesity and central nervous system leptin uptake involves a combination of a saturable and an unsaturable mechanism. CSF NPY and alpha-MSH did not differ from controls in human obesity, and the CSF NPY level decreased significantly whereas alpha-MSH did not differ after weight loss in obese subjects compared with baseline. There was no significant correlation between CSF leptin and CSF NPY or alpha-MSH. This could be the result of leptin resistance present in human obesity and/or the more complex mechanisms involved in modulating appetite and regulating energy balance in human obesity.

Adult↗

Absence of constitutively activating mutations in the GHRH receptor in GH-producing pituitary tumors.

The molecular events leading to the development of GH-producing pituitary tumors remain largely unknown. We hypothesized that activating mutations of the GHRH receptor might occur in a subset of GH-producing pituitary tumors. Genomic DNA samples from 54 GH-producing pituitary tumor tissues were screened for mutations of the GHRH receptor. Eleven homozygous or heterozygous nucleotide substitutions [169G > A (A57T), 338C > T (P113L), 363G > T (E121D), 409C > T (H137Y), 547G > A (D183N), 673G > A (V225I), 749G > A (W250X), 760G > A (V254M), 785G > A (S262N), 880G > A (G294R), 1268G > A (C423Y)] were found in 12 patients (22.2%). The 169G > A substitution (A57T) appears to be a polymorphism (4 patients, 7.4%). E121D and V225I were each found in 2 patients. In 1 patient with the V225I sequence, the substitution was not found in genomic DNA from peripheral leukocytes, suggesting a somatic mutation. A patient with a heterozygous W250X mutation was homozygous for the C423Y substitution. These variant GHRH receptors were studied in transfected TSA-201 cells to evaluate the functional consequences of the amino acid changes. None of the GHRH receptor variants was associated with basal elevation of intracellular cAMP. GHRH induced variable cAMP responses. With the W250X and G294R variants, there was no cAMP stimulation by GHRH, indicating that the mutations are inactivating. Expression of the W250X GHRH receptor on the cell membrane was severely decreased and GHRH binding to the G294R GHRH receptor was impaired. Although GHRH receptor variants are common in GH- producing pituitary adenomas, constitutively activating mutations, as a mechanism for GH-producing pituitary tumors appear to be rare.

Amino Acid Sequence↗

An anemic patient with phenotypical beta-thalassemic trait has elevated level of structurally normal beta-globin mRNA in reticulocytes.

Of the numerous beta-thalassemic mutations linked or unlinked to the beta-globin gene, all invariably cause a decrease in or an absence of structurally normal beta-globin mRNA when assayed. Here we report an anemic patient with an elevated alpha-/beta globin synthesis ratio of 2.0 in his reticulocytes. The patient's blood film showed marked red cell anisopoikilocytosis, microcytosis, and hypochromia, consistent with a typical beta-thalassemic trait phenotype. Acid-eluted erythrocytes contained numerous Heinz bodies. Molecular analysis of the patient's reticulocyte mRNA indicated that, compared to normal controls, there was a 3-fold elevation of beta-globin mRNA when assayed by RT-PCR and a 1.5-fold elevation of beta-globin mRNA when assayed by RNA slot blotting. The level of alpha-globin mRNA was normal when compared to that of normal adult controls. Extensive structural analysis of the beta-globin mRNA and gene by sequencing of RT-PCR and PCR products, respectively, did not detect any mutations. Tryptic mapping of purified beta-globin chains also did not show any abnormal tryptic fragments. These data indicated that a relative insufficiency of structurally normal beta-globin mRNA was not a cause of this beta-thalassemic phenotype. Therefore, the lesion that caused this particular thalassemic phenotype is not linked to the beta-globin allele.

Anemia↗

Identification of glucokinase mutation in subjects with post-renal transplantation diabetes mellitus.

Mutations in the glucokinase (GCK) gene are considered to be a possible cause of maturity-onset diabetes of the young. The purpose of this study was to evaluate the contribution of this gene to the development of post-renal transplantation diabetes mellitus (PTDM). Identification of the GCK mutation was attempted in 58 selected renal allograft recipients with PTDM and 45 normal controls. The exons in the GCK gene were examined using polymerase chain reaction (PCR), followed by an analysis of single-stranded DNA conformational polymorphism (SSCP). The abnormal bands were then confirmed by DNA sequencing analysis. The family members of the patients affected with GCK mutation were also examined. Two of the 58 PTDM patients (3. 4%) were found to have GCK mutations. One had the mutation on exon 5 and the other on intron 7. One control subject had the mutation on intron 9. The mutation on exon 5 was identified as a substitution of CCT (proline) for CTT (leucine) at codon 164, which has never been reported before. The family members of the PTDM patient with a mutation on exon 5 were analyzed by PCR, followed by SSCP, and two of them had the same mutation. The abnormal band seen on SSCP analysis of exon 7 was identified as the C-->T substitution at the 39th nucleotide in intron 7. Two of the family members also displayed the same bands on the SSCP. One of the 45 normal controls had a known polymorphism located at the 8th nucleotide in intron 9. We found a GCK mutation on the exon in subjects with PTDM and we speculate that this mutation may be one of the possible contributing factors of PTDM, although variations of the GCK gene are not common causes of PTDM.

Adult↗

Haptoglobin reduces renal oxidative DNA and tissue damage during phenylhydrazine-induced hemolysis.

BACKGROUND: Haptoglobin knockout (Hp-/-) mice are more sensitive to phenylhydrazine-induced hemolysis than Hp+/+ mice. METHODS: Hemolysis was induced in Hp-/- and Hp+/+ mice using phenylhydrazine. Relative renal tissue damage and function were then assessed. RESULTS: Hp-/- mice had higher basal levels of renal lipid peroxidation, as evidenced by levels of malonaldehyde and 4-hydroxy-2(E)-nonenal (MDA/HNE). After the administration of phenylhydrazine, levels of 8-hydroxyguanine (but not other products of oxidative DNA damage) were significantly elevated in the renal DNA. There was also increased induction of heme oxygenase-1. The more severe renal damage in Hp-/- mice was also evident in the delayed erythropoietin gene expression and poorer renal clearance of 3H-inulin. This reduction in glomerular filtration function in Hp+/+ and Hp-/- mice could be restored to baseline by vasodilators (prazosin or diazoxide), implicating renal vasoconstriction as a major mechanism of acute renal failure during induced hemolysis. Precipitation of hemoglobin in the kidney was not increased in Hp-/- mice. CONCLUSIONS: Haptoglobin appears to play an important physiological role as an antioxidant, particularly during hemolysis.

Acute-Phase Reaction↗

Chronic alcohol intake differently influences glucose metabolism according to nutritional status.

We investigated the potential different effects of a chronic alcohol intake on glucose metabolism according to nutritional status in growing rats. Eighty weanling 4-week-old male Sprague Dawley rats were fed with low (5%, wt/wt) or control (22%) protein diet for 8 weeks. Each group was subdivided into alcohol (5 g/kg(-1) x day(-1)) or saline gavage rats during the last 4 weeks. At 12 weeks of age, we measured the weights of the body, pancreas, and epididymal fat; glycogen synthase activity of gastrocnemius muscle; and insulin content of the pancreas. We performed an ip glucose tolerance test and a euglycemic hyperinsulinemic clamp test. Weight gain was almost arrested in protein-deficient rats. The relative weight and insulin content of the pancreas and glycogen synthase activity were not different among the four groups, but the relative amount of epididymal fat decreased only in protein-deficient saline rats. Insulin response after glucose challenge and glucose disposal rate during the euglycemic clamp were both markedly decreased in protein-deficient saline rats, but not changed in protein-deficient alcohol rats. Protein-deficiency per se causes deterioration both in insulin secretory function and in sensitivity, but these defects are protected by a chronic alcohol intake. In a protein-sufficient state, alcohol intake gives no additional effects on glucose metabolism. Therefore, according to individual nutritional status, the metabolic effect of alcohol intake appears differently.

Adipose Tissue↗

Effects of cyclosporin A on sex hormone and estrogen receptor in male rat with special reference to cyclosporin A-induced osteoporosis.

The mechanisms of high turnover bone loss induced by Cyclosporin A (CsA) are not clearly understood. Deficiencies in sex hormones result in high turnover osteoporosis, and not only androgen but also estrogen plays an important role in maintaining bone mass in men. To study whether or not there are any changes in the levels of sex hormones, aromatization, and the expression of estrogen receptors in CsA-induced osteoporosis, we treated 39 rats with vehicle, low-dose CsA (5 mg/kg) and high dose CsA (15 mg/kg) for 28 days, and measured sex hormone levels by radioimmunoassay. Aromatase activities in ROS cells and 3T3-L1 cells were determined by measuring the conversion rate of 3H-androstenedione into 3H-estrone. ER and ER mRNA were measured by competitive RT-PCR in collected marrow cells and ROS cells. The levels of free testosterone in the serum in low-dose CsA-treated rats were unchanged, but the levels were significantly decreased in those treated with high-dose CsA as previously reported. The levels of total estradiol in the serum were significantly increased in the low-dose CsA-treated group (5 mg/kg) and were comparable to levels of the control group in the high-dose CsA-treated group (15 mg/kg). CsA increased the conversion of 3H-androstenedione to 3H-estrone in ROS cells, but not in 3T3-L1 cells. Meanwhile, CsA treatment did not change the rates of ER or ER mRNA expression in ROS cells or in collected bone marrow cells. In conclusion, CsA treatment decreased the level of free testosterone in the serum, but did not decrease the level of serum estradiol by enhancing aromatization. High-turnover osteoporosis induced by clinical dosage CsA treatment may not be caused by lowering the levels of circulating estrogen or by decreasing the expression of estrogen receptors.

3T3 Cells↗

Type I beta-turn conformation is important for biological activity of the melanocyte-stimulating hormone analogues.

In order to define which structure of alpha-melanocyte-stimulating hormone (MSH) analogues plays a critical role for ligand-receptor interaction and selectivity, we analysed receptor-binding and cAMP-generating activity in Chinese hamster ovary cell lines stably transfected with rMC3R and hMC4R, as well as the NMR structures of chemically synthesized alpha-MSH analogues. Compared with [Ahx4]alpha-MSH, the linear MTII designated as alpha-MSH-ND revealed a preference for the MC4R, whereas its IC50 and EC50 values were comparable to those of MTII reported previously. Truncation of Ahx4 and Asp5 of alpha-MSH-ND remarkably decreased the receptor-binding and cAMP-generating activity. Meanwhile, maximum cAMP-generating activity was observed at a higher concentration (10(-5) M) of alpha-MSH-ND(6-10), and MC4R preference was changed into MC3R preference. In contrast, [Gln6]alpha-MSH-ND(6-10) lost its cAMP-generating activity almost completely, even though it bound to both receptors. Whereas the solution conformation of alpha-MSH-ND revealed a stable type I beta-turn structure, [Gln6]alpha-MSH-ND(6-10) revealed a tight gamma-turn composed of Gln6-D-Phe7-Arg8. Replacement of the His6 residue of alpha-MSH-ND by Gln, Asn, Arg or Lys decreased not only the receptor binding, but also the cAMP-generating activity in both the MC3R and the MC4R. The structure of [Gln6]alpha-MSH-ND exhibited a stable type I' beta-turn comprising Asp5, Gln6, D-Phe7 and Arg8. [Lys6]alpha-MSH-ND showed a greatly reduced binding affinity and cAMP-generating activity with the loss of MC4R selectivity. In NMR studies, [Lys6]alpha-MSH-ND also demonstrated a gamma-turn conformation around Lys6-DPhe7-Arg8. From the above results, we conclude that a type I beta-turn conformation comprising the residues Asp5-His6-(D-Phe7)-Arg8 was important for receptor binding and activation, as well as the selectivity of MSH analogues.

Animals↗

A Na(+)-dependent system A and ASC-independent amino acid transport system stimulated by glucagon in rat hepatocytes.

The effects of glucagon on amino acid transport in rat hepatocytes are not fully understood. We examined the effect of this hormone on alanine, serine and cysteine preferring system (system ASC)-mediated amino acid transport in rat hepatocyte monolayers using 2-aminoisobutyric acid (AIB) and l -cysteine. Glucagon induced a time and protein synthesis-dependent stimulation of Na(+)-dependent alanine preferring system (system A)-independent AIB transport. The glucagon-induced increase in transport activity was not modified by substrate starvation and not related to changes in the intracellular pool of amino acids. Glucagon did not modify system ASC activity measured by l -cysteine. Therefore the transport activity of AIB independent of system A stimulated by glucagon cannot be attributed to system ASC. This suggests a Na(+)-dependent transport system in rat hepatocytes not identified until now.

Amino Acids↗

Reduced erythropoietin responsiveness to anemia in diabetic patients before advanced diabetic nephropathy.

We often encounter diabetic patients with anemia in whom the causes of anemia were not clearly identified despite differential hematologic studies. We therefore studied the clinical and biochemical characteristics of diabetic patients with anemia of uncertain cause and measured erythropoietin (Epo) concentrations in 35 diabetic subjects without significant diabetic renal disease. Among 62 medical records of diabetic patients with anemia, showing no evidence of advanced diabetic nephropathy (creatinine clearance > or = 30 mg/kg/1.73 m2), the causes of the anemia were not able to be identified in 28 cases (45.2%). In addition, we enrolled 35 diabetic patients with uncertain causes of anemia in order to evaluate the serum Epo responsiveness to anemia, and compared levels to a group of non-diabetic subjects also with anemia. The serum Epo concentrations of diabetic patients (17.6 +/- 8.1 mIU/ml) were significantly lower than those of non-diabetic patients with similar degree of decrease in hemoglobin concentrations (144.9 +/- 108.0 mIU/ml, P<0.001). The hemoglobin concentrations of diabetic patients correlated with creatinine clearance (r = 0.34, P = 0.03), serum creatinine (r = -0.49, P = 0.003) and albumin excretion rate (r = -0.44, P = 0.009), but showed no relation to age, duration of diabetes, glycated hemoglobin, presence of retinopathy or neuropathy. We concluded that reduced Epo responsiveness to anemia could explain the anemia present in diabetic patient but without advanced diabetic nephropathy. This may reflect early renal interstitial damage.

Aged↗

Low-dose growth hormone treatment with diet restriction accelerates body fat loss, exerts anabolic effect and improves growth hormone secretory dysfunction in obese adults.

Growth hormone (GH) can induce an accelerated lipolysis. Impaired secretion of GH in obesity results in the consequent loss of the lipolytic effect of GH. Dietary restriction as a basic treatment for obesity is complicated by poor compliance, protein catabolism, and slow rates or weight loss. GH has an anabolic effect by increasing insulin-like growth factor (IGF)-I. We investigated the effects of GH treatment and dietary restriction on lipolytic and anabolic actions, as well as the consequent changes in insulin and GH secretion in obesity. 24 obese subjects (22 women and 2 men; 22-46 years old) were fed a diet of 25 kcal/kg ideal body weight (IBW) with 1.2 g protein/kg IBW daily and were treated with recombinant human GH (n = 12, 0.18 U/kg IBW/week) or placebo (n = 12, vehicle injection) in a 12-week randomized, double-blind and placebo-controlled trial. GH treatment caused a 1.6-fold increase in the fraction of body weight lost as fat and a greater loss of visceral fat area than placebo treatment (35.3 vs. 28.5%, p < 0.05). In the placebo group, there was a loss in lean body mass (-2.62 +/- 1.51 kg) and a negative nitrogen balance (-4.52 +/- 3.51 g/day). By contrast, the GH group increased in lean body mass (1.13 +/- 1.04 kg) and had a positive nitrogen balance (1.81 +/- 2.06 g/day). GH injections caused a 1.6-fold increase in IGF-I, despite caloric restriction. GH response to L-dopa stimulation was blunted in all subjects and it was increased after treatment in both groups. GH treatment did not induce a further increase in insulin levels during an oral glucose tolerance test (OGTT) but significantly decreased free fatty acid (FFA) levels during OGTT. The decrease in FFA area under the curve during OGTT was positively correlated with visceral fat loss. This study demonstrates that in obese subjects given a hypocaloric diet, GH accelerates body fat loss, exerts anabolic effects and improves GH secretion. These findings suggest a possible therapeutic role of low-dose GH with caloric restriction for obesity.

Adipose Tissue↗

A PCR analysis of ERalpha and ERbeta mRNA abundance in rats and the effect of ovariectomy.

To study the relative abundance and the changes of both estrogen receptor alpha (ERalpha) and ERbeta mRNA before and after ovariectomy in major organs important to the regulation of calcium homeostasis, we compared the degree of mRNA expression of ERalpha to that of ERbeta in rat tissues by performing competitive reverse transcription polymerase chain reaction (RT-PCR) with internal standards. Both ERalpha and ERbeta were highly expressed in the ovary {ERalpha[(2.2 +/- 0.33) x 10(7) copies/microg of total RNA] > ERbeta[(1.2 +/- 0.33) x 10(5) copies/microg of total RNA]} as we expected. The bone marrow and renal cortex were very important target organs of estrogen because ERalpha was highly expressed approximately 2 x 10(5) copies/microg of total RNA, but marrow cells revealed only a very weak expression of ERbeta [(0.7 +/- 0.21) x 10(2) copies/microg of total RNA]. Both ERalpha and ERbeta were expressed in the trabecular bone [(3.2 +/- 0.56) x 10(3) copy/microg of RNA] and [(2.8 +/- 0.21) x 102 copy/microg of RNA], respectively. However, they were not detected in the cortical bone. In the jejunum, the expression of ERalpha was not detectable, while ERbeta was expressed very weakly [(1.1 +/- 0.24) x 10(2) copies/microg of total RNA]. The thyroid gland expressed low copy numbers of ERbeta [(6.0 +/- 0.23) x 10(2) copies/microg of total RNA], but the parathyroid gland was negative for both ERalpha and ERbeta mRNA. In cultured stromal cells, ERalpha and ERbeta mRNAs were not detected after a 24-h culture; however, the rates of mRNA expression of ERalpha and ERbeta reached approximately 105 copies/microg of total RNA and approximately 10(2) copies/microg of total RNA, respectively, after 9-, 11-, and 13-day cultures. After ovariectomy, the expression of ERalpha mRNA decreased abruptly in the bone marrow and renal cortex, and both ERalpha and ERbeta were barely detected in the trabecular bone. In conclusion, ERalpha might be the main ER in organs important for calcium homeostasis, except in the jejunum. The mRNA expression of ERalpha in the bone marrow and renal cortex decreased abruptly after ovariectomy, which may partially explain why the effect of estrogen deficiency can be amplified and why trabecular bone loss is more predominant than cortical bone loss shortly after surgical or natural menopause.

Animals↗