De novo synthesis of lipids and incorporation of oleic acid into cultured human fibroblasts from diabetics and normal controls

Fibroblasts from type 1 diabetics exhibit enhanced Ca(2+) mobilization after TNF or fat exposure

The effects of cytokine and fatty acid treatment on signal transduction in dermal fibroblasts from type 1 diabetics and matched controls were compared. Chronic exposure to TNF, accentuated Ca²⁺ mobilization in response to bradykinin (BK) in cells from both controls and diabetics; responses were three-fold greater in cells from diabetics than in controls. Similarly, with chronic exposure to IL-1β, BK-induced Ca²⁺ mobilization was accentuated in cells from type 1 diabetics compared to the controls. Pretreatment with the protein synthesis inhibitor cycloheximide or the protein kinase C inhibitor calphostin C prior to the addition of TNF completely abrogated the TNF-induced increment in peak bradykinin response. Ca²⁺ transients induced by depleting endoplasmic reticulum (ER) Ca²⁺ with thapsigargin were also greater in TNF treated fibroblasts than in untreated cells, with greater increases in cells from diabetics. Exposing fibroblasts for 48 hours to 2 mM oleate also increased both the peak bradykinin response and the TNF-induced increment in peak response, which were significantly greater in diabetics than controls. These data indicate that cells from diabetic patients acquire elevated ER Ca²⁺ stores in response to both cytokines and free fatty acids,and thus exhibit greater sensitivity to environmental inflammatory stimuli and elevated lipids.

Episodes of severe metabolic acidosis in a patient with 3-methylglutaconic aciduria

Persistent excretion of 3-methylglutaconic acid was found in a 6-month-old infant with multiple minor physical malformations and delayed development. During two episodes of intercurrent viral illness, the patient developed severe metabolic acidosis and excreted large amounts of lactate, 3-hydroxybutyrate and acetoacetate. The excretion of 3-methylglutaconic acid did not change during these episodes, nor did it increase following leucine loading. In vitro studies suggest that in this patient, as in the majority of other patients with 3-methylglutaconic aciduria, a primary defect in leucine metabolism is not responsible for the biochemical abnormality.

Myotonic dystrophy: studies on the lipid composition and metabolism of erythrocytes and skin fibroblasts

With the aim of establishing the underlying biochemical lesion in myotonic dystrophy, the lipids of plasma and of the membranes of erythrocytes and cultured skin fibroblasts were investigated in patients with this disorder and normal age- and sex-matched controls. No qualitative or quantitative differences could be detected in the lipid constituents of either plasma or erythrocytes from patients and controls. Similar growth characteristics and levels of sodium [1-14C]acetate incorporation were found in skin fibroblasts from both groups when grown in medium supplemented with either normal serum or delipidated serum. It is concluded that despite the previous evidence that drug induced myotonia results from a primary disturbance of membrane lipids, and suggestions that myotonic dystrophy might have a similar basis, our results did not support this hypothesis. They do not however exclude a primary membrane enzyme abnormality as the basic defect for the disorder.

Comparative studies on human skin fibroblasts: life span and lipid metabolism in medium containing fetal bovine or human serum

Three strains of human skin fibroblasts were cultivated in nutrient medium supplemented either with human serum or fetal bovine serum, and growth and lipid synthesis were compared. Rates of cellular growth were similar in both kinds of medium, but the replicative life spans of all three strains were curtailed significantly in human-serum medium. Incorporation of label into the major classes of neutral lipids from [14C]acetate and 3H2O was increased also in human-serum medium. Since human serum contained higher concentrations of cholesterol known to reduce endogenous cholesterol synthesis, these results were unexpected. Nonlipid factors in human serum may account for the shortened cellular life spans and increased lipogenesis and perhaps for the potential to develop atherosclerosis.