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Biomedical subjects

M K Lee

Publications and source records attributed to M K Lee.

At least 55 records · Page 3Linked to original sources
PubMed2001

Five novel neuroprotective triterpene esters of Ulmus davidiana var. japonica.

Investigation of the constituents of the stem and root barks of Ulmus davidiana var. japonica resulted in the isolation of five new triterpene esters named ulmicin A-E (1-5). Using several spectroscopic techniques, their structures were determined to be 3beta,11alpha,15alpha-trihydroxylup-20(29)-ene-11-(3'-methoxy-4'-hydroxybenzoyl ester) (1), 3beta,11alpha,15alpha-trihydroxylup-20(29)-ene-11-(4'-hydroxybenzoyl ester) (2), 3beta,11alpha,15alpha-trihydroxylup-20(29)-ene-11-(3'-methoxy-4'-hydroxybenzoyl)-15-(4'-hydroxybenzoyl ester) (3), 3beta,11alpha,15alpha-trihydroxylup-20(29)-ene-11,15-di(3'-methoxy-4'-hydroxybenzoyl ester) (4), and 3beta,11alpha,15alpha-trihydroxylup-20(29)-ene-11-(3'-methoxy-4'-hydroxybenzoyl)-15-(benzoyl ester) (5). All five compounds showed significant neuroprotective activities against glutamate-induced neurotoxicity in primary cultures of rat cortical cells.

Animals↗
PubMed2001

Interactive effect of hesperidin and vitamin E supplements on cholesterol metabolism in high cholesterol-fed rats.

Certain bioflavonoids are potent antioxidants and have pharmacologic effects similar to those of vitamin E. Accordingly, the interactive effect of hesperidin and vitamin E was studied with respect to cholesterol metabolism and the antioxidant status. Hesperidin supplement (0.1%, wt/wt) with comparable levels of vitamin E was provided with a high-cholesterol (1%, wt/wt) diet to rats for 5 weeks. The amount of vitamin E included in the hesperidin-free and hesperidin diets was either a low (low-E) or a normal (normal-E) level. The hesperidin supplement and different levels of dietary vitamin E did not significantly alter the concentrations of plasma triglycerides. However, the inclusion of hesperidin significantly lowered the concentration of plasma cholesterol in both the low-vitamin E group and the normal-vitamin E group compared to the hesperidin-free groups (p < 0.05). The hepatic triglyceride content was significantly lowered by the hesperidin supplement, as opposed to the plasma triglyceride content, regardless of the vitamin E level in the diet. The hepatic HMG-CoA reductase activity was significantly lowered by the hesperidin supplement with both the low-vitamin E and the normal-vitamin E compared to the hesperidin-free groups (p < 0.05). The hepatic HMG-CoA reductase activity was also significantly lowered with an increase in the dietary vitamin E within the hesperidin and hesperidin-free groups. The excretion of fecal neutral sterol and acidic sterols tended to be lower with the hesperidin supplement. Neither dietary hesperidin nor vitamin E significantly changed the hepatic antioxidant enzyme activity. This data indicates that hesperidin lowers the concentration of plasma cholesterol and the hepatic triglyceride content regardless of the dietary vitamin E level. However, the concentration of plasma cholesterol in the hesperidin-free groups was dependent on the dietary vitamin E level. This information may contribute to understanding the interactive effect of hesperidin and vitamin E on cholesterol biosynthesis in high cholesterol-fed rats.

Animals↗
PubMed2001

Antibacterial, antitumor and hemolytic activities of alpha-helical antibiotic peptide, P18 and its analogs.

The alpha-helical antibiotic peptide (P18: KWKLFKKIPKFLHLAKKF-NH2) designed from the cecropin A(1-8)-magainin 2 (1-12) hybrid displayed strong bactericidal and tumoricidal activity without inducing hemolysis. The effect of the Pro9 residue at central position of P18 on cell selectivity was investigated by Pro9 --> Leu or Pro9 --> Ser substitution. Either substitution markedly reduced the antibacterial activity of P18 and increased hemolysis, although it did not significantly affect cytotoxicity against human transformed tumor and normal fibroblast cells. These results suggest that a proline kink in alpha-helical antibiotic peptide P18 serves as a hinge region to facilitate ion channel formation on bacterial cell membranes and thus plays an important role in providing high selectivity against bacterial cells. Furthermore, to investigate the structure-antibiotic activity relationships of P18, a series of N- or C-terminal deletion and substitution analogs of P18 were synthesized. The C-terminal region of P18 was related to its antibiotic activity and alpha-helical conformation on lipid membranes rather than N-terminal one. Higher alpha-helicity of the peptides was involved in the hemolytic and antitumor activity rather than antibacterial activity. Except for [L9]-P18 and [S9]-P18, all the designed peptides containing a Pro residue showed potent antibacterial activity, although they did not induce a cytolytic effect against human erythrocyte and normal fibroblast cells at the concentration required to kill bacteria. In particular, P18 and some analogs (N-1, N-2, N-3, N-3L and N-4L) with potent bactericidal and tumoricidal activity and little or no normal cell toxicity may serve as an attractive candidate for the development of novel anti-infective or antitumor agents.

Amino Acid Sequence↗
PubMed2001

Single dose radiation is more effective for the UV-induced activation and proliferation of melanocytes than fractionated dose radiation.

PURPOSE: To establish whether the effect of fractionating radiation modifies the effects of ultraviolet (UV) radiation on epidermal melanocytes, we compared the clinical and histological effects of single high dose radiation against repeated intermediate to low dose radiation on epidermal melanocytes. METHODS: Three minimal erythema UV doses (MED) were administered to three sites on the buttocks of healthy volunteers. One site was irradiated with 0.5 MED UV every day for 6 consecutive days, another site was irradiated with 1 MED UV every second day, and a third site received a single dose of radiation with 3 MED UV. The treatment was replicated on the other buttock. For the evaluation of UV-induced erythema and pigmentation, erythema and melanin indices were measured at 2 and 14 days post-irradiation. For purposes of histological evaluation, tissue specimens taken from each irradiated site at 2 and 14 days post-irradiation and were stained with monoclonal antibodies against Mel-5, HMB-45 and tyrosinase. Fontana-Masson silver staining, DOPA staining and split DOPA reactions were also performed. RESULTS: At 14 days post-irradiation, UV radiation induced melanocyte activation, proliferation and melanogenesis in proportion to the radiation dose administered to each fraction. The most prominent responses were observed after single high doses of radiation. CONCLUSION: When the total administered dose is identical, fractionation of radiation dose diminishes the effects of UV radiation on epidermal melanocytes. Furthermore, long, uninterrupted doses of UV radiation were found to more effective in inducing melanogenesis and melanocyte activation.

Adult↗
PubMed2001

Modulation of skin collagen metabolism in aged and photoaged human skin in vivo.

To the best of our knowledge, no study has been conducted to date to directly compare the collagen metabolism of photoaged and naturally aged human skin. In this study, we compared collagen synthesis, matrix metalloproteinase-1 levels, and gelatinase activity of sun-exposed and sun-protected skin of both young and old subjects. Using northern blot analysis, immunohistochemical stain, and Western blot analysis, we demonstrated that the levels of procollagen type I mRNA and protein in photoaged and naturally aged human skin in vivo are significantly lower than those of young skin. Furthermore, we demonstrated, by northern blot analysis, that the procollagen alpha1(I) mRNA expression of photoaged skin is much greater than that of sun-protected skin in the same individual. In situ hybridization and immunohistochemical stain were used to show that the expression of type I procollagen mRNA and protein in the fibroblasts of photoaged skin is greater than for naturally aged skin. In addition, it was found, by Western blot analysis using protein extracted from the dermal tissues, that the level of procollagen type I protein in photoaged skin is lower than that of naturally aged skin. The level of matrix metalloproteinase-1 protein and the activity of matrix metalloproteinase-2 were higher in the dermis of photoaged skin than in naturally aged skin. Our results suggest that the natural aging process decreases collagen synthesis and increases the expression of matrix metalloproteinases, whereas photoaging results in an increase of collagen synthesis and greater matrix metalloproteinase expression in human skin in vivo. Thus, the balance between collagen synthesis and degradation leading to collagen deficiency is different in photoaged and naturally aged skin.

Adult↗
PubMed2001

Rapid species identification of coagulase negative Staphylococci by rRNA spacer length polymorphism analysis.

OBJECTIVES: The identification of coagulase-negative staphylococci (CNS) is carried out mainly through conventional methods, commercial identification kits, and molecular biology-based methods. We evaluated the efficiency of PCR analysis of tRNA intergenic spacer length polymorphism (tDNA-ILP) and 16S-23S intergenic spacer length polymorphism (16S-23S ILP), and also that of restriction analysis of 16S-23S intergenic spacer amplification products (RA 16S-23S), for the rapid and accurate identification of CNS species. METHODS: The PCR assays of rRNA spacer length polymorphisms were tested with nine reference type strains and 122 clinical isolates. The results were compared with those obtained by conventional methods and the Vitek system for clinical isolates. RESULTS: Seventy-eight (63.9%) of 122 strains were identified as the same species with conventional identification, the Vitek GPI system, tDNA-ILP, and RA 16S-23S. The 16S-23S ILP analysis did not produce distinguishable PCR fragments. The results of tDNA-ILP analysis were in agreement with those of RA 16S-23S to the species level for 98.2% except for unknown patterns (eight isolates). CONCLUSIONS: These results indicate that tDNA-ILP and RA 16S-23S analysis are potentially valuable tools for rapid and accurate CNS identification.

Coagulase↗
PubMed2001

Insulin secretory dysfunction and insulin resistance in the pathogenesis of korean type 2 diabetes mellitus.

Although insulin resistance has been shown to be a primary defect causing type 2 (non insulin-dependent) diabetes mellitus in Pima Indians and Caucasians, insulin secretory defect has also been known to be an important factor in the development of type 2 diabetes. We undertook a study to investigate the initial abnormality of glucose intolerance in Koreans. A total of 370 Korean subjects were classified into 5 groups according to their degree of glucose intolerance (normal fasting glucose [NFG]/normal glucose tolerance [NGT], n = 95; impaired fasting glucose [IFG]/NGT, n = 29; NFG/impaired glucose tolerance [IGT], n = 60; IFG/IGT, n = 68; diabetes, n = 118). Insulinogenic index was used as an index of early-phase insulin secretion. Insulin resistance was assessed by the R value of the homeostasis model assessment [HOMA(R)]. Insulinogenic index significantly decreased in subjects with IFG/NGT and NFG/IGT compared with those with NFG/NGT. However, there was no significant difference in HOMA(R) between subjects with NFG/NGT and those with IFG/NGT or NFG/IGT. Insulinogenic index decreased significantly with the increase of plasma glucose 120-minute value at the earlier stage of glucose intolerance compared with HOMA(R). These results suggest that early-phase insulin secretory defect may be the initial abnormality in the development of type 2 diabetes in Korean subjects.

Adult↗
PubMed2001

Effects of hydrastine derivatives on dopamine biosynthesis in PC12 cells.

The effects of hydrastine derivatives on dopamine biosynthesis in PC12 cells were investigated. Treatments of PC12 cells with (1R,9S)-beta-hydrastine hydrochloride [(+)-beta-hydrastine HCl] and (1R,9S)-beta-hydrastine [(-)-beta-hydrastine] showed 50.6 % and 33.1 % inhibition of dopamine content at a concentration of 10 microM for 48 h. However, (1S,9R)-beta-hydrastine [(+)-beta-hydrastine] and hydrastinine hydrochloride did not reduce dopamine content. The IC(50) values of (1R,9S)-beta-hydrastine hydrochloride and (1R,9S)-beta-hydrastine were 9.3 microM and 20.7 microM , respectively. Next, the intracellular mechanisms of (1R,9S)-beta-hydrastine hydrochloride in PC12 cells were investigated. Dopamine content decreased at 6 h and reached a minimal level at 24 h after the exposure of PC12 cells to 20 microM (1R,9S)-beta-hydrastine hydrochloride. Tyrosine hydroxylase (TH) activity was inhibited at 6 h following the treatment with (1R,9S)-beta-hydrastine hydrochloride, and was maintained at a reduced level for up to 36 h in PC12 cells (17 - 27 % inhibition at 20 microM), whereas TH mRNA level was not found to alter for 24 h. However, the level of intracellular Ca++ concentration decreased by treatment with (1R,9S)-beta-hydrastine hydrochloride at 20 microM by 18.4 % inhibition relative to the control level in PC12 cells. These results suggest that (1R,9S)-beta-hydrastine hydrochloride contributes partially to the decrease in dopamine content by the inhibition of TH activity in PC12 cells.

Alkaloids↗
PubMed2001

Terfenadine-beta-Cyclodextrin inclusion complex with antihistaminic activity enhancement.

Terfenadine, an antihistaminic drug, has relatively low bioavailability after oral administration due to its limited solubility in water. To enhance the antihistaminic activity of terfenadine, the terfenadine-beta-cyclodextrin (1:2) inclusion complex was prepared by the neutralization method. The solubility and dissolution of the inclusion complex were carried out, and its antihistaminic activity was then evaluated and compared with terfenadine powder by the passive subcutaneous anaphylaxis method in rats. The formation constant of the inclusion complex was higher at lower pH, while its formation ratio was 1:2 irrespective of pH. For terfenadine, it improved the solubility 200 times and the dissolution rate 5 times. It gave a low histamine level at 30 min, followed by a sustained low level until 60 min, while terfenadine powder gave a low histamine level at 60 min, suggesting that it had faster and more effective antihistaminic activity than terfenadine powder in rats due to fast dissolution and absorption of terfenadine. It is concluded that this inclusion complex enhanced the antihistaminic activity of terfenadine following the enhanced solubility and dissolution of terfenadine.

Algorithms↗
PubMed2001

Routine measurement of serum calcitonin is useful for early detection of medullary thyroid carcinoma in patients with nodular thyroid diseases.

BACKGROUND: Medullary thyroid carcinoma (MTC) is characterized by a high concentration of serum calcitonin. Routine measurement of serum calcitonin concentration has been advocated for detection of MTC among patients with nodular thyroid diseases. However, a minimal to moderate increase of serum calcitonin concentration has been frequently observed in diseases other than MTC. Fine-needle aspiration cytology (FNAC) is not a reliable method for detection of MTC. Therefore, we evaluated the usefulness of routine measurement of serum calcitonin concentration in patients with nodular thyroid diseases, and studied the validity of pentagastrin stimulation test and FNAC in these patients. SUBJECTS AND METHODS: We performed routine measurement of serum calcitonin concentrations in 1,448 patients (male, 285, female, 1,163) with nodular thyroid diseases. The average age was 46 years (range, 14-86 years). Initial examination included thyroid examination, thyroid scan or ultrasonography, measurements of serum free triiodothyronine) (T3), free thyroxine (T4), thyrotropin (TSH) levels, and antithyroid autoantibodies. FNAC was performed in all patients who had palpable or visible thyroid nodule by ultrasonography, and pentagastrin stimulation test was performed in 39 patients who consented. Serum calcitonin concentration was measured with a two-site immunoradiometric assay using commercial kits. We also measured the serum calcitonin concentration in 407 healthy subjects without thyroid or nonthyroid diseases. RESULTS: Serum calcitonin concentration was 10 pg/mL or less in 403 normal subjects (99.0 percentile), and 11-13 pg/mL in the remaining 4 subjects. We found that 56 (3.87%) of 1,448 patients with nodular thyroid diseases had serum calcitonin level above 10 pg/mL. Ten patients (0.69%) with histologically confirmed MTC were detected by the routine measurement of serum calcitonin. The prevalence of MTC was 5.2% in 194 patients with thyroid carcinoma. Five of 10 patients with MTC had basal serum calcitonin level above 100 pg/mL. The remaining 5 patients had minimal or moderate elevation of basal serum calcitonin (range, 12-86 pg/mL). Serum calcitonin concentration increased to more than 100 pg/mL by pentagastrin in all patients with MTC (2.4- to 37.7-fold increase). FNAC suggested MTC in only 2 patients (22.2%), and failed to diagnose MTC in 7 patients. FNAC was not performed in 1 patient with MTC, because he had no visible mass by ultrasonography. CONCLUSION: These results suggested that routine measurement of serum calcitonin is useful in the early detection of MTC among patients with nodular thyroid diseases. Pentagastrin stimulation test may also be a reliable way for evaluating thyroid nodular patients with mild or moderate elevation of serum calcitonin concentrations. However, FNAC was not sensitive in detecting MTC. We recommend routine measurement of serum calcitonin concentration in patients with nodular thyroid diseases.

Adolescent↗
PubMed2001

Deep desulfurization of extensively hydrodesulfurized middle distillate oil by Rhodococcus sp. strain ECRD-1.

Dibenzothiophene (DBT), and in particular substituted DBTs, are resistant to hydrodesulfurization (HDS) and can persist in fuels even after aggressive HDS treatment. Treatment by Rhodococcus sp. strain ECRD-1 of a middle distillate oil whose sulfur content was virtually all substituted DBTs produced extensive desulfurization and a sulfur level of 56 ppm.

Biodegradation, Environmental↗
PubMed2001

N-linked glycosylation sites adjacent to and within the V1/V2 and the V3 loops of dualtropic human immunodeficiency virus type 1 isolate DH12 gp120 affect coreceptor usage and cellular tropism.

The envelope glycoprotein of human immunodeficiency virus type 1 (HIV-1) is extensively glycosylated, containing approximately 23 asparagine (N)-linked glycosylation sites on its gp120 subunit. In this study, specific glycosylation sites on gp120 of a dualtropic primary HIV-1 isolate, DH12, were eliminated by site-directed mutagenesis and the properties of the resulting mutant envelopes were evaluated using a recombinant vaccinia virus-based cell-to-cell fusion assay alone or in the context of viral infections. Of the glycosylation sites that were evaluated, those proximal to the V1/V2 loops (N135, N141, N156, N160) and the V3 loops (N301) of gp120 were functionally critical. The glycosylation site mutations near the V1/V2 loop compromised the use of CCR5 and CXCR4 equally. In contrast, a mutation within the V3 loop preferentially inhibited the usage of CCR5; although this mutant protein completely lost its CCR5-dependent fusion activity, it retained 50% of the wild-type fusion activity with CXCR4. The replication of a virus containing this mutation was severely compromised in peripheral blood mononuclear cells, MT-4 cells, and primary monocyte-derived macrophages. A revertant virus, which acquired second site changes in the V3 loop that resulted in an increase in net positive charge, was isolated. The revertant virus fully recovered the usage of CXCR4 but not of CCR5, thereby altering the tropism of the parental virus from dualtropic to T-tropic. These results suggest that carbohydrate moieties near the V1/V2 and the V3 loops play critical roles in maintaining proper conformation of the variable loops for optimal interaction with receptors. Our results, combined with those of previously reported studies, further demonstrate that the function of individual glycans may be virus isolate dependent.

Base Sequence↗
PubMed2001

Polyvalent envelope glycoprotein vaccine elicits a broader neutralizing antibody response but is unable to provide sterilizing protection against heterologous Simian/human immunodeficiency virus infection in pigtailed macaques.

The great difficulty in eliciting broadly cross-reactive neutralizing antibodies (NAbs) against human immunodeficiency virus type 1 (HIV-1) isolates has been attributed to several intrinsic properties of their viral envelope glycoprotein, including its complex quaternary structure, extensive glycosylation, and marked genetic variability. Most previously evaluated vaccine candidates have utilized envelope glycoprotein from a single virus isolate. Here we compare the breadth of NAb and protective immune response following vaccination of pigtailed macaques with envelope protein(s) derived from either single or multiple viral isolates. Animals were challenged with Simian/human immunodeficiency virus strain DH12 (SHIV(DH12)) following priming with recombinant vaccinia virus(es) expressing gp160(s) and boosting with gp120 protein(s) from (i) LAI, RF, 89.6, AD8, and Bal (Polyvalent); (ii) LAI, RF, 89.6, AD8, Bal, and DH12 (Polyvalent-DH12); (iii) 89.6 (Monovalent-89.6); and (iv) DH12 (Monovalent-DH12). Animals in the two polyvalent vaccine groups developed NAbs against more HIV-1 isolates than those in the two monovalent vaccine groups (P = 0.0054). However, the increased breadth of response was directed almost entirely against the vaccine strains. Resistance to SHIV(DH12) strongly correlated with the level of NAbs directed against the virus on the day of challenge (P = 0.0008). Accordingly, the animals in the Monovalent-DH12 and Polyvalent-DH12 vaccine groups were more resistant to the SHIV(DH12) challenge than the macaques immunized with preparations lacking a DH12 component (viz. Polyvalent and Monovalent-89.6) (P = 0.039). Despite the absence of any detectable NAb, animals in the Polyvalent vaccine group, but not those immunized with Monovalent-89.6, exhibited markedly lower levels of plasma virus than those in the control group, suggesting a superior cell-mediated immune response induced by the polyvalent vaccine.

AIDS Vaccines↗
PubMed2001

Effects of Puerariae Flos and Puerariae Radix extracts on antioxidant enzymes in ethanol-treated rats.

This study was performed to investigate the effect of Puerariae Flos (PF) and Puerariae Radix (PR) water extracts on the activities and mRNA expression of three hepatic antioxidant enzymes in ethanol-treated rats. Male Sprague-Dawley rats were divided into four groups, a control, ethanol-treated, ethanol plus PF-treated, and ethanol plus PR-treated group with seven rats per group. Ethanol (25 % v/v, 5 g/kg body weight) was orally administered once a day for 5 weeks. The PF and PR water extracts were supplemented in a diet based on 1.2 g of raw PF or PR/kg body weight/day. Ethanol administration without the PF or PR supplement significantly lowered the activities of hepatic Cu/Zn SOD and catalase (CAT), whereas it increased the hepatic GSH-Px activity. However, the PF and PR supplementation resulted in a significant increase in the Cu/Zn SOD and/or CAT activities and a significant decrease in the GSH-Px activity in the ethanol-treated rats. The mRNA levels of these antioxidant enzymes in the ethanol-treated rats were normalized to the control level by the PF or PR supplement. The hepatic glutathione content, which was significantly lower in the ethanol-treated group than in the control group, was also normalized to the control level by supplementing with either PF or PR. The PF or PR supplement resulted in lowering the hepatic malondialdehyde to the control level in the ethanol-treated rats.

Animals↗
PubMed2001

Effect of naringin supplementation on cholesterol metabolism and antioxidant status in rats fed high cholesterol with different levels of vitamin E.

Some bioflavonoids are potent antioxidants and have pharmacological effects similar to those of vitamin E. The interactive effect of naringin and vitamin E was studied with respect to cholesterol metabolism and antioxidant status. Naringin supplementation (0.1%, wt/wt) with comparable levels of vitamin E was given to rats with a high-cholesterol (1%, wt/wt) diet for 5 weeks. The amount of vitamin E included in naringin-free and naringin diets was a low (low-E) and a normal (normal-E) level. The naringin supplementation significantly lowered the concentrations of plasma cholesterol and triglyceride compared to the naringin-free group in low vitamin E-fed rats. HMG-CoA reductase activity was significantly lowered by naringin supplementation within both the low-vitamin E group (794.64 +/- 9.87 vs. 432.18 +/- 12.33 pmol/min/mg protein, mean +/- SE; p < 0.05) and normal-vitamin E group (358.82 +/- 11.4 vs. 218.22 +/- 9.47 pmol/min/mg protein, mean +/- SE; p < 0.05) compared to each of the naringin-free group. The HMG-CoA reductase activity was also significantly lowered by increased dietary vitamin E when compared within the naringin and naringin-free group, respectively. Neither dietary naringin nor vitamin E did significantly change the activities of hepatic antioxidant enzymes and plasma thiobarbituric acid-reactive substance level. These data indicate that naringin lowers the plasma lipid concentrations when the dietary vitamin E level is low. The HMG-CoA reductase-inhibitory effect of naringin was more potent when dietary vitamin E was at a normal level. These data may contribute to understanding the interactive effect of naringin and vitamin E on cholesterol biosynthesis in high-cholesterol-fed rats.

Animals↗
PubMed2001

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↗