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J A Cuthbert

Publications and source records attributed to J A Cuthbert.

At least 55 records · Page 3Linked to original sources
PubMed1987

Regulation of lymphocyte proliferation by cholesterol: the role of endogenous sterol metabolism and low density lipoprotein receptors.

Cholesterol availability is a major determinant of the capacity of lymphocytes to proliferate. Either endogenously-synthesized cholesterol or that taken up from the medium can be utilized as a source for new membrane biosynthesis. Mitogenic stimulation of human lymphocytes augments the rate of endogenous sterol synthesis. This mitogen-induced increase in lymphocyte sterol synthesis can be observed within 4 h of stimulation and is prevented by suppressing the activity of 3-hydroxy-3-methyl-glutaryl coenzyme A (HMG-CoA) reductase with the specific inhibitors ML-236B or mevinolin. The resultant inhibition of lymphocyte sterol synthesis does not affect mitogen-stimulated blast transformation or initial entry into the S phase of the cell cycle, even when no source of exogenous sterol is present. However, maximal enlargement of the stimulated blast cells is suppressed by inhibition of HMG-CoA reductase activity, and lymphocyte proliferation is completely prevented. These inhibitory effects are reversed by the addition either of mevalonate, the product of the inhibited enzyme, or of low-density-lipoprotein (LDL) cholesterol. The finding that LDL cholesterol could not support growth of lymphocytes obtained from individuals who lacked LDL receptors indicates that LDL-mediated delivery of exogenous sterols to proliferating lymphocytes requires intact LDL receptors. The data indicate that neither endogenous sterol synthesis nor a source of cholesterol is necessary for mitogen-stimulated activation and blast transformation of human lymphocytes. Subsequent enlargement and cell division requires either sterol synthesis or an exogenous source of cholesterol. When the exogenous source of cholesterol is in the form of LDL, normal LDL receptors are also necessary.

Cell Cycle↗
PubMed1986

Low-density lipoprotein (LDL) and lymphocyte responses: direct suppression by native LDL and indirect inhibition from zinc chelation by contaminating EDTA.

Low-density lipoproteins (LDL) have been shown to have a number of effects on the function of various cell types. To appreciate whether the in vitro effects of LDL have in vivo relevance, it is necessary to demonstrate that the biologic action described can be accounted for by native LDL and not by an alteration in the molecule or an addition to the preparation occurring during isolation. EDTA is frequently added to LDL during preparation to prevent oxidation. The effect of EDTA dialysis on LDL-mediated inhibition of lymphocyte responses was therefore examined. LDL alone did not inhibit mitogen-induced initial lymphocyte activation but rather suppressed lymphocyte DNA synthesis and subsequent proliferation in a transferrin-reversible manner. LDL dialysed with EDTA also inhibited lymphocyte responsiveness but the inhibition was not reversed by transferrin. Further experiments demonstrated that after dialysis EDTA in the LDL accounted for the change in its inhibitory effects. EDTA did not alter the lipoprotein but itself inhibited lymphocyte responses by chelating zinc necessary for DNA synthesis. These data indicate that LDL preparations may exhibit at least two separate effects on lymphocyte function. LDL is directly suppressive, while small amounts of contaminating EDTA can additionally be suppressive by chelating zinc. Thus, EDTA present in LDL preparations can alter their apparent biologic effects.

Adult↗
PubMed1986

Detection of familial hypercholesterolemia by assaying functional low-density-lipoprotein receptors on lymphocytes.

In familial hypercholesterolemia, structural and functional abnormalities of the receptor for low-density lipoprotein (LDL) lead to hypercholesterolemia and premature atherosclerosis. We have developed a simplified method to identify LDL-receptor defects in peripheral-blood lymphocytes. When lymphocytes are cultured in lipoprotein-depleted medium and endogenous sterol biosynthesis is suppressed with mevinolin, mitogen-stimulated proliferation of lymphocytes is dependent on an exogenous source of cholesterol. Whereas a small concentration of supplemental LDL cholesterol (3 to 4 micrograms per milliliter) permits a maximal response in normal lymphocytes, even high concentrations (10 to 50 micrograms per milliliter) are unable to support the proliferation of lymphocytes from patients with homozygous familial hypercholesterolemia. Thus, functional LDL receptors are necessary to allow lymphocyte proliferation in these cultures. The response of lymphocytes from patients with hyperlipidemia not caused by defective LDL receptors was like that of normal cells. In contrast, the response of lymphocytes from patients with heterozygous familial hypercholesterolemia was intermediate between that of homozygotes and that of normal or hyperlipidemic controls. Our method can therefore be used to identify persons who are heterozygous for abnormalities of LDL receptors.

Cells, Cultured↗
PubMed1986

Promotion of human T lymphocyte activation and proliferation by fatty acids in low density and high density lipoproteins.

Mitogen-induced lymphocyte DNA synthesis measured by [3H]thymidine incorporation and lymphocyte proliferation assessed by counting the number of cells were reduced by greater than 95% when cells were cultured at low density in the absence of serum. Supplementation with either transferrin or lipoprotein alone only partially restored lymphocyte responses. Addition of both transferrin and lipoproteins of each major subclass permitted mitogen-induced lymphocyte DNA synthesis and proliferation equal to that observed in serum-containing medium. The degree of enhancement was dependent on the concentration of the lipoprotein added and could not be explained by the nonspecific addition of protein to the defined medium. The mechanisms of growth promotion by various lipoprotein fractions did not appear to be explained by provision of cholesterol to the cells. Neither cholesterol nor cholesteryl ester from endogenous sources or supplied exogenously was able to enhance mitogen-induced lymphocyte responses. In contrast, fatty acids, phospholipid, and triglyceride alone supported lymphocyte responses. Furthermore, lipoproteins retained the capacity to enhance lymphocyte responses following extraction of neutral lipid. Both low density lipoprotein and high density lipoprotein, subclass 3, increased the number of cells initially activated by mitogenic stimulation and supported the subsequent continued growth of the activated cells. Low density lipoprotein was more efficient than high density lipoprotein, subclass 3, in this latter regard. These results indicate that lipoproteins can promote maximal growth of mitogen-activated lymphocytes in transferrin-containing medium by providing growth factors other than cholesterol necessary for initial activation and required for continued lymphocyte proliferation.

Cell Division↗
PubMed1986

Acute local irritative effect of (2''R)-4'-O-tetrahydropyranyladriamycin, a new antitumor antibiotic.

(2"R)-4'-O-Tetrahydropyranyladriamycin hydrochloride (THP), a new antitumor antibiotic, was administered to rabbits at a concentration from 0.02 to 0.5% by instillation, or by intracutaneous, subcutaneous or intramuscular injection to study its local irritative effect. The irritative effect of THP increased with concentration. At a concentration of 0.5%, THP was irritant to the eye, skin and muscle but at a concentration of 0.1% practically no effect was observed. The effect was equal to or lower than that of doxorubicin. An instillation of 0.5% THP caused reversible irritation effect on the eye. Slight conjunctival responses (redness and chemoisis) were observed. Rinsing reduced the irritative effect. Intracutaneous injection of 0.1 ml of 0.5% THP caused well defined, moderate erythema, surface ulceration and dermal necrosis. Cutaneous muscle necrosis also occurred. At a concentration of 0.02%, dermal necrosis and inflammatory cell infiltration were observed. Erythema, as well as muscle necrosis and calcification with giant cell reaction and inflammatory cell infiltration were observed by an intramuscular injection at a concentration of 0.5%. Subcutaneous injection of 0.5% THP showed no irritative effect.

Animals↗
PubMed1984

Modulation of human lymphocyte responses by low density lipoproteins (LDL): enhancement but not immunosuppression is mediated by LDL receptors.

The role of low density lipoprotein (LDL) receptors in mediating the immunomodulatory effects of LDL was examined by comparing responses of normal lymphocytes with those obtained from a patient with familial hypercholesterolemia (FH) lacking receptors for LDL. The function of LDL receptors in supporting lymphocyte growth was demonstrated by blocking endogenous sterol synthesis with mevinolin, a specific inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, and culturing cells in lipoprotein-deficient medium with supplemental LDL as the only source of cholesterol. Mevinolin inhibited mitogen-induced proliferation of normal and FH lymphocytes. Whereas inhibition was overcome by mevalonate, the product of the inhibited enzyme, low concentrations of LDL (less than 10 micrograms of protein/ml) restored the responses of normal but not FH lymphocytes. When normal and FH lymphocytes were cultured in the absence of mevinolin, high concentrations of LDL (greater than 100 micrograms of protein/ml) inhibited mitogen-induced lymphocyte proliferation. The inhibitory effects on normal and FH lymphocytes were similar in that both required comparably large concentrations of LDL and could be completely reversed by transferrin. When normal lymphocytes were cultured in serum-free medium supplemented with transferrin, low concentrations of LDL (less than 10 micrograms of protein/ml) caused marked augmentation of proliferation. By contrast, no enhancement of FH lymphocyte growth was observed. These results indicate that LDL-mediated enhancement of lymphocyte growth in the presence or absence of endogenous sterol biosynthesis involves specific receptors for LDL whereas the immunosuppression caused by LDL is independent of these receptors. Moreover, the results suggest that peripheral lymphocytes can be used to evaluate the functional integrity of the receptor-mediated uptake of LDL.

Child↗
PubMed1984

Immunoregulation by low density lipoproteins in man. Inhibition of mitogen-induced T lymphocyte proliferation by interference with transferrin metabolism.

Human low density lipoprotein (LDL, d = 1.020-1.050 g/ml) inhibits mitogen-stimulated T lymphocyte DNA synthesis. Because both LDL and transferrin bind to specific cell surface receptors and enter cells by the similar means of receptor-mediated endocytosis, and because transferrin is necessary for lymphocyte DNA synthesis, we investigated the possibility that LDL may inhibit mitogen-stimulated lymphocyte responses by interfering with transferrin metabolism. LDL inhibited mitogen-stimulated lymphocyte [3H]thymidine incorporation in a concentration-dependent manner. The degree of inhibition was most marked in serum-free cultures, but was also observed in serum-containing cultures. The addition of transferrin not only augmented mitogen-induced lymphocyte [3H]thymidine incorporation in serum-free medium but also completely reversed the inhibitory effect of LDL in both serum-free and serum-containing media. Similar results were obtained when lymphocyte proliferation was assayed by counting the number of cells in culture. Transferrin also reversed the inhibition of lymphocyte responses caused by very low density lipoproteins and by cholesterol. The ability of transferrin to reverse the inhibitory effect of lipoproteins was specific, in that native but not denatured transferrin was effective whereas a variety of other proteins were ineffective. These results indicate that LDL inhibits mitogen-stimulated lymphocyte responses by interfering with transferrin metabolism. LDL only inhibited lymphocyte responses after a 48-h incubation if present from the initiation of the culture. By contrast, transferrin reversed inhibition when added after 24 h of the 48-h incubation. LDL did not inhibit lymphocyte responses by nonspecifically associating with transferrin. In addition, the acquisition of specific lymphocyte transferrin receptors was not blocked by LDL. Moreover, transferrin did not prevent the binding and uptake of fluorescent-labeled LDL by activated lymphocytes. Furthermore, LDL did not prevent the binding of transferrin to its receptor. Finally, LDL inhibition did not require specific high affinity cell surface receptors for cholesterol transport by LDL because similar inhibition and reversal by transferrin were observed with lymphocytes from a patient with homozygous familial hypercholesterolemia. Thus, LDL alters lymphocyte responses in a non-LDL receptor-mediated way by interfering with transferrin metabolism after specific binding of transferrin to receptors on activated lymphocytes.

Adult↗
PubMed1983

Microtubules and lymphocyte responses: effect of colchicine and taxol on mitogen-induced human lymphocyte activation and proliferation.

The role of microtubules in mitogen-induced human lymphocyte activation and proliferation was examined. The effect of colchicine, a microtubule-disrupting agent, was compared with taxol, a microtubule-stabilizing drug, and with isaxonine (N-isopropyl-amino-2-pyrimidine orthophosphate), a proposed microtubular-active drug. Lymphocyte proliferation, assessed by measuring the increase in the number of cells in mitogen-stimulated cultures, was completely suppressed by both colchicine and taxol (100 nM) whereas significant inhibition by isaxonine required much higher concentrations (5 mM). In order to characterize the inhibition, initial lymphocyte blast transformation and subsequent DNA synthesis were investigated. Neither colchicine nor taxol inhibited lymphocyte blast transformation assessed by quantitating the change in volume of the stimulated cells after a 24-hour incubation. In contrast, isaxonine (2-5 mM) suppressed blast transformation. Initial DNA synthesis, evaluated by measuring the cumulative incorporation of [3H]thymidine between 30 and 48 hours of culture, was inhibited in a concentration-dependent manner by both isaxonine and colchicine but not by taxol. Electron microscopic studies confirmed that both taxol and colchicine (10 nM) arrested the responding lymphocytes in mitosis, and that isaxonine inhibited initial activation. These results suggest that normal microtubule function is only necessary for cell division and that drug effects on blast transformation and initial DNA synthesis are unrelated to microtubules.

Adult↗
PubMed1983

Immunoregulation by low density lipoproteins in man: low density lipoprotein inhibits mitogen-stimulated human lymphocyte proliferation after initial activation.

Low density lipoprotein (LDL, d 1.020-1.050 g/ml), isolated from normal human plasma by ultracentrifugation, inhibited mitogen-stimulated proliferation of human lymphocytes in a concentration-dependent manner. In order to characterize the inhibition more fully, the effect of LDL on initial lymphocyte activation and subsequent DNA synthesis was investigated. LDL had no effect on lymphocyte blast transformation assessed by quantitating the change in volume of the stimulated cells after a 24-hour incubation. Moreover, initial lymphocyte activation assessed by mitogen-stimulated RNA or protein synthesis was not inhibited by LDL. Finally, the acquisition of transferrin or T cell growth factor receptors by the activated lymphocytes was not affected by LDL. DNA synthesis, evaluated by measuring the incorporation of [3H]thymidine between 30 and 48 hours of culture was inhibited by LDL in a concentration-dependent manner. The DNA content of individual mitogen-stimulated cells was analyzed by flow cytometry after mithramycin staining. These studies confirmed that LDL inhibited DNA synthesis in the initially activated lymphocytes. In addition, LDL in concentrations that did not inhibit initial DNA synthesis did suppress cell division and lymphocyte proliferation. These results indicate that LDL inhibits lymphocyte responses by exerting inhibitory effects on DNA synthesis, cell division, and subsequent growth of the activated cells rather than by altering initial lymphocyte blast transformation. LDL thus may play a role in regulating clonal expansion of activated lymphocytes during immune responses.

Adult↗
PubMed1981

A prospective trial of steroid therapy in severe viral hepatitis. The prognostic significance of bridging necrosis.

A prospective, double-blinded, randomized trial of corticosteroid therapy in patients with severe acute viral hepatitis has been conducted. At the same time, we have examined the prognostic significance of the presence of bridging necrosis in liver biopsies obtained from such patients as well as the predictive value of certain serologic markers. Forty-two of the 77 patients admitted to the trial were shown to have bridging necrosis on their initial biopsies. Two patients progressed to death with massive hepatic necrosis, while 5 patients developed chronic liver disease. A complicated course could not be predicted by the initial biopsy findings nor by any of the serologic markers assessed. We could not identify any clinical or epidemiologic features with prognostic impact. No advantage was demonstrated to be associated with the use of corticosteroids early in the course of severe viral hepatitis.

Adolescent↗
PubMed1979

Etiology of liver disease in renal-transplant patients.

The etiology of 72 episodes of liver disease that developed in 62 of 162 renal-transplant recipients was evaluated. Infection with hepatitis B virus was a minor problem, and none of our patients had evidence of infection with hepatitis A. Cytomegalovirus infection was ubiquitous in the population and probably accounted for many episodes of acute liver disease. This agent's role in causing chronic hepatitis is less secure. Infections with other viruses including Epstein-Barr virus, adenovirus, and the herpes viruses were only rarely associated with hepatic disease. Azathioprine was responsible for some episodes of acute cholestasis but could not be incriminated as a direct cause of chronic disease. A cause could be identified for the majority of episodes of acute hepatic dysfunction, but the cause of most of the chronic hepatitis remains undetermined. It is likely that infection with non-A, non-B hepatitis virus accounts for much of this serious, often fatal, complication of renal transplantation.

Antibodies, Viral↗
PubMed1978

Colonic and oesophageal disturbance in a patient with multiple endocrine neoplasia, type 2b.

We report the illness of a 32-year-old male with the syndrome of multiple endocrine neoplasia, type 2b, which comprises medullary carcinoma of the thyroid, phaeochromocytoma, oral mucosal neuromas and skeletal deformity. The patient also had evidence of ganglioneuromatosis of the alimentary tract, a finding which is held to be responsible for constipation and a number of the other gastrointestinal manifestations of the MEN, 2b. Dysphagia, which has not been previously reported in the syndrome was also present. Investigations of the oesophagus which included endoscopy, radiology and a motility study support the diagnosis of achalasia as the cause of the dysphagia.

Adrenal Gland Neoplasms↗