Colchicine inhibition of insulin induction of stearoyl-CoA desaturase and fatty acid synthetase in cultured avian liver explants

Colchicine is a safe drug in children with familial Mediterranean fever

OBJECTIVE

To identify any adverse effects of colchicine in a pediatric patients with familial Mediterranean fever (FMF).

STUDY DESIGN

Clinical presentation, Mediterranean fever gene genotype, disease duration, colchicine dose, laboratory tests, and reported adverse effects in children with FMF were analyzed.

RESULTS

Of the 153 patients with FMF, 22 (14.4%) developed diarrhea during a follow-up of 4 years; the colchicine dose was reduced to control this symptom in only 4 patients. In 18 (11.8%) patients, a mild transitory increase of transaminases (45-158 IU/L) was found during a follow-up of 1 year. Blood cell counts and kidney function tests were normal in all patients. No correlation was found between the adverse effects and patient's age, disease onset, treatment duration, or any of the clinical characteristics of the disease.

CONCLUSION

Colchicine is a safe drug in the treatment of children with FMF, even in infancy. The only significant adverse effects are diarrhea (in a small number of patients), which can be controlled by a decrease in the colchicine dose and transitory elevation of transaminases.

Microtubular integrity differentially modifies the saturated and unsaturated fatty acid metabolism in cultured Hep G2 human hepatoma cells

The influence of cytoskeleton integrity on the metabolism of saturated and unsaturated FA was studied in surface cultures and cell suspensions of human Hep G2 hepatoma cells. We found that colchicine (COL), nocodazol, and vinblastin produced a significant inhibition in the incorporation of labeled saturated FA, whereas incorporation of the unsaturated FA remained unaltered. These microtubule-disrupting drugs also diminished Delta9-, Delta5-, and Delta6-desaturase capacities. The effects produced by COL were dose (0-50 microM) and time (0-300 min) dependent, and were antagonized by stabilizing agents (phalloidin and DMSO). Dihydrocytochalasin B (20 microM) was tested as a microfilament-disrupting drug and produced no changes in either the incorporation of [14C] FA or the desaturase conversion of the substrates. We hypothesized that the interactions between cytoskeleton and membrane proteins such as FA desaturases may explain the functional organization, facilitating both substrate channeling and regulation of unsaturated FA biosynthesis.

Microtubule involvement in translational regulation of fibronectin expression by light chain 3 of microtubule-associated protein 1 in vascular smooth muscle cells

Our previous studies suggested that enhanced fibronectin mRNA translation in ductus arteriosus compared with aortic smooth muscle cells is related to increased expression of light chain 3 (LC3) of microtubule-associated protein 1, which binds an AU-rich element in the 3' untranslated region of fibronectin mRNA. We therefore hypothesized that microtubules are involved in LC3-mediated fibronectin mRNA translational regulation. In this study we show that disruption of microtubules by colchicine inhibits fibronectin mRNA translation in cultured ductus arteriosus smooth muscle cells. We proposed that the mechanism might be related to decreased docking of fibronectin mRNA on the translational machinery, ie, membrane-bound polysomes on rough endoplasmic reticulum, and confirmed this by Northern blot analysis. To investigate the mechanism further, we carried out polysome analysis using sucrose gradient centrifugation and fractionation and studied the polysomal distribution of fibronectin mRNA and LC3 protein in the sucrose gradient by using RNase protection assay and Western immunoblotting, respectively. Colchicine treatment shifts fibronectin mRNA from the fractions containing membrane-bound polysomes to the fractions carrying free polysomes and concomitantly decreases the amount of LC3 protein in the fractions containing membrane-bound polysomes. Furthermore, an EDTA-release experiment demonstrates that LC3 protein associates with the 60S ribosomal subunit. Our data support the concept that microtubules may function with LC3 to facilitate sorting of fibronectin mRNA onto rough endoplasmic reticulum and translation.

Sequence analysis and characterization of FAR-17c, an androgen-dependent gene in the flank organs of hamsters

This study reports on the isolation and characterization of a cDNA clone, regulated by androgen transcriptionally, in male Golden hamsters' flank organs. Previous studies have reported on the cloning of an androgen-dependent gene, FAR-17a, from the same hamster organ. After castration, the FAR-17c transcription rate decreases faster than FAR-17a but is not suppressed completely. The recovery of transcription by androgen injection is also faster than FAR-17a. In male hamsters, it is expressed strongly in the sebaceous glands and liver, and weakly in the lungs and brain. It has never been expressed in the testes. In the female, it is strongly expressed in the liver and brain and weakly in the lungs and flank organs. Sequence analysis shows that FAR-17c has a long 1062 bp open reading frame and its deduced amino acid sequence (354 residues) is highly homologous to the stearyl-CoA desaturases of the rat liver and mouse adipocytes. Stearyl-CoA desaturase, either in the liver or adipocytes appears to be independent of androgen regulation. Since stearyl-CoA desaturase plays a key role in fatty acid metabolism, further studies on its regulation by androgen are warranted in relation to acne vulgaris.

The regulation of stearoyl-CoA desaturase (SCD)

The stearoyl-CoA desaturase gene family encodes stearoyl-CoA desaturase, the key enzyme involved in the biosynthesis of unsaturated fatty acids, as well as in the regulation of this process. Because of the important role that the SCD gene product plays in fat cell metabolism, future studies on SCD1 gene expression could provide new insights into the role of fatty acids in cellular regulation, metabolism, and gene expression both in normal and disease states. In addition, the SCD gene family can be used as a model to study mechanisms of cellular differentiation, tissue-specific gene expression, and dietary and hormonal regulation of gene expression.

Alteration of microtubule physiology in hepatocytes by insulin

Incubation of primary cultures of rat hepatocytes with insulin caused an alteration in several parameters of microtubule physiology. There was a transient decrease in total cellular tubulin levels and, at the same time, an apparent stabilization of microtubule polymers which was also transient. The level of microtubule polymer, however, was not altered, which indicated that an insulin-inducible decrease in the level of nonpolymerized tubulin was responsible for the decrease in total cellular tubulin. These changes were followed by an increase in tubulin mRNA levels and, shortly thereafter, by an increase in tubulin protein synthesis. This study demonstrates that microtubule physiology in hepatocytes is modulated by insulin and, further, suggests a model by which insulin-induced changes in microtubule physiology may play a role in regulating other insulin responses.

A sigmoidal relationship between liver stearoyl CoA desaturase activity and serum hormone concentrations caused by streptozocin and its antagonists

Stearoyl CoA desaturase activity in liver microsomes, and insulin, thyroxine, and triiodothyronine levels in serum were measured after administration of streptozocin (STZ) and its antagonists to rats. The effect of STZ, which caused hyperglycemia and inhibited the desaturase activity, was antagonized by 2-desoxyglucose and 3-O-methyl-glucose; 1-O-methyl-3-desoxyglucose and 1-O-methyl-3-O-methylglucose were without any effect. The enzyme activity plotted against insulin levels showed a broad sigmoidal curve, whereas the activities versus thyroid hormone levels showed steeper sigmoidal curves.