Metformin treatment of antipsychotic-induced dyslipidemia: an analysis of two randomized, placebo-controlled trials.

Dyslipidemia is one of the most common adverse effects in schizophrenia patients treated with antipsychotics. However, there are no established effective treatments. In this study, data were pooled from two randomized, placebo-controlled trials, which were originally designed to examine the efficacy of metformin in treating antipsychotic-induced weight gain and other metabolic abnormalities. In total, 201 schizophrenia patients with dyslipidemia after being treated with an antipsychotic were assigned to take 1000 mg day-1 metformin (n=103) or placebo (n=98) for 24 weeks, with evaluation at baseline, week 12 and week 24. The primary outcome was the low-density lipoprotein cholesterol (LDL-C) levels. After metformin treatment, the mean difference in the LDL-C value between metformin treatment and placebo was from 0.16 mmol l-1 at baseline to -0.86 mmol l-1 at the end of week 24, decreased by 1.02 mmol l-1 (P<0.0001); and 25.3% of patients in the metformin group had LDL-C ≥3.37 mmol l-1, which is significantly <64.8% in the placebo group (P<0.001) at week 24. Compared with the placebo, metformin treatment also have a significant effect on reducing weight, body mass index, insulin, insulin resistance index, total cholesterol and triglyceride, and increasing high-density lipoprotein cholesterol. The treatment effects on weight and insulin resistance appeared at week 12 and further improved at week 24, but the effects on improving dyslipidemia only significantly occurred at the end of week 24. We found that metformin treatment was effective in improving antipsychotic-induced dyslipidemia and insulin resistance, and the effects improving antipsychotic-induced insulin resistance appeared earlier than the reducing dyslipidemia.

Tropomodulin-binding site mapped to residues 7-14 at the N-terminal heptad repeats of tropomyosin isoform 5.

Tropomodulin is a globular protein that caps the pointed end of actin filaments by complexing with the N-terminus of a tropomyosin (TM) molecule. TM consists of coiled coils except for the N-terminus, which may be globular. Here we report that human TM isoform 5 (hTM5) lacking the N-terminal 18 residues lost its binding activity toward tropomodulin. We further characterized the tropomodulin-binding site by creating a series of deletion and missense mutations within this region, followed by a solid-phase binding assay. I7, V10, and I14, hydrophobic residues located at the a and d positions of N-terminal heptad repeats involving intertwine, are essential for tropomodulin binding. R12, a positively charged residue at the f position, is also involved in recognition. In contrast, A2R and G3Y mutations, each creating a bulky N-terminus, did not alter the binding. In addition, rat TM5b, which differs from hTM5 in residues 4-6, exhibits a similar binding affinity. The tropomodulin-binding site, therefore, is mapped to residues 7-14 at the beginning of the long heptad repeats. Column chromatography revealed that hTM5 mutants remained capable of dimerization. Results also suggest tropomodulin has a groove-type, rather than a cavity-type, binding site for hTM5. We also mapped the epitope of monoclonal antibody LC1 to residues 4-10 of hTM5 and showed the competition between mAb LC1 and tropomodulin in hTM5 binding. Since the N-terminal residues need to overlap with the C-terminus of TM in their head-to-tail association, this investigation elucidates the mechanisms by which the tropomodulin-hTM5 complex is formed and functions in regulating the actin filaments.

Tropomyosin isoform 5b is expressed in human erythrocytes: implications of tropomodulin-TM5 or tropomodulin-TM5b complexes in the protofilament and hexagonal organization of membrane skeletons.

The human erythrocyte membrane skeleton consists of hexagonal lattices with junctional complexes containing F-actin protofilaments of approximately 33-37 nm in length. We hypothesize that complexes formed by tropomodulin, a globular capping protein at the pointed end of actin filaments, and tropomyosin (TM), a rod-like molecule of approximately 33-35 nm, may contribute to the formation of protofilaments. We have previously cloned the human tropomodulin complementary DNA and identified human TM isoform 5 (hTM5), a product of the gamma-TM gene, as one of the major TM isoforms in erythrocytes. We now identify TM5b, a product of the alpha-TM gene, to be the second major TM isoform. TM5a, the alternatively spliced isoform of the alpha-TM gene, which differs by 1 exon and has a weaker actin-binding affinity, however, is not present. TM4, encoded by the delta-TM gene, is not present either. In sodium dodecyl sulfate-polyacrylamide gel electrophoresis, hTM5 comigrated with the slower TM major species in erythrocyte membranes, and hTM5b comigrated with the faster TM major species. TM5b, like TM5, binds strongly to tropomodulin, more so than other TM isoforms. The 2 major TM isoforms, therefore, share several common features: They have 248 residues, are approximately 33-35 nm long, and have high affinities toward F-actin and tropomodulin. These common features may be the key to the mechanism by which protofilaments are formed. Tropomodulin-TM5 or tropomodulin-TM5b complexes may stabilize F-actin in segments of approximately 33-37 nm during erythroid terminal differentiation and may, therefore, function as a molecular ruler. TM5 and TM5b further define the hexagonal geometry of the skeletal network and allow actin-regulatory functions of TMs to be modulated by tropomodulin. (Blood. 2000;95:1473-1480)

Metabolic effects of troglitazone on fat-induced insulin resistance in the rat.

Troglitazone is a new orally active hypoglycemic agent that has been shown to ameliorate insulin resistance and hyperinsulinemia in both diabetic animal models and non-insulin-dependent diabetes mellitus (NIDDM) subjects. To determine whether this drug could prevent the development of diet-induced insulin resistance and related abnormalities, we studied its effect on insulin resistance induced by high-fat feeding in rats. Normal male Sprague-Dawley rats were fed a high-fat diet for 3 weeks with and without troglitazone as a food mixture (0.2%) or were fed normal chow. In vivo insulin action was measured using a euglycemic-hyperinsulinemic clamp at two different insulin infusion rates, 4 (submaximal stimulation) and 40 (maximal stimulation) mU/kg/min. Fat feeding markedly reduced the submaximal glucose disposal rate ([GDR], 26.4 +/- 1.3 v 37.5 +/- 1.4 mg/kg/min, P < .01) and maximal GDR (55.9 +/- 1.3 v 64.5 +/- 1.3 mg/kg/min, P < 0.5), reduced the suppressibility of submaximal hepatic glucose production ([HGP], 3.2 +/- 0.9 v 1.5 +/- 0.5 mg/kg/min, P < .05), and resulted in hyperlipidemia. Troglitazone treatment did not affect any of these parameters. Insulin resistance induced by fat feeding is the first experimental model in which troglitazone failed to correct or partially correct the insulin resistance.

Metabolic effects of troglitazone on fructose-induced insulin resistance in the rat.

Troglitazone is a new orally active hypoglycemic agent that has been shown to reduce insulin resistance and hyperinsulinemia in both diabetic animal models and non-insulin-dependent diabetes mellitus (NIDDM) subjects. To determine whether this drug could prevent the development of fructose-induced insulin resistance and related abnormalities, we studied the effects of troglitazone on the insulin resistance induced by fructose feeding in rats. Normal male Sprague-Dawley rats were fed a high-fructose diet for 3 weeks with and without troglitazone as a food admixture (0.2%) or were fed normal chow to serve as a control group. In vivo insulin resistnace was measured by the euglycemic hyperinsulinemic clamp technique at two different insulin infusion rates, 29 (submaximal stimulation) and 290 (maximal stimulation) pmol.kg-1.min-1. Fructose feeding markedly reduced submaximal glucose disposal rate (GDR) (113.8 +/- 8.3 vs. 176.0 +/- 5.6 mumol.kg-1.min-1, P < 0.05) and maximal GDR (255.9 +/- 5.6 vs. 313.6 +/- 10.5 mumol.kg-1.min-1, P < 0.05), reduced the suppressibility of submaximal hepatic glucose production (HGP; 45.5 +/- 5.0 vs. 11.7 +/- 5.0 mumol.kg-1.min-1, P < 0.05), and resulted in hypertriglyceridemia and hypertension. Troglitazone treatment completely restored the GDR (submaximal 158.2 +/- 5.6, maximal 305.3 +/- 6.1 mumol.kg-1.min-1) and submaximal HGP (9.4 +/- 2.8 mumol.kg-1.min-1) to control levels and also normalized the elevated plasma triglyceride concentration and systolic blood pressure levels in fructose-fed rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Responses of neurones in the nucleus paragigantocellularis lateralis to somatic nerve stimulation.

Among the seventy-eight extracellularly recorded neurones in the nucleus paragigantocellularis lateralis (PGL), 30 and 31 of them were excited by the stimulation of superficial (SPN) and deep (DPN) peroneal nerve, respectively. In the other 17 neurones, convergent inputs from both nerves to a single neurone were found, and a post-excitatory inhibition was also observed. The consequence of the integrated responses to the stimulation of both nerves depended on the time interval of the stimuli to them. Excitatory post-synaptic potentials (EPSP) were recorded in neurones excited by the stimulation of both nerves. In conclusion, the stimulation of SPN and DPN can excite neurones in PGL, at least partially, via EPSP through their respective pathways; the integrated responses of PGL neurones to both nerves are related to the arrival time of impulses from them.

Post-synaptic activity evoked in the rostral ventrolateral medullary neurones by stimulation of the defence areas of hypothalamus and midbrain in the rat.

Neurones in the rostral ventrolateral medulla (RVLM) of the rat were recorded intracellularly (n = 30) and extracellularly (n = 91) in vivo. 91% of them had spontaneous activity with frequencies of 1.1-29.9 Hz. Onset latencies of the excitation induced by the stimulation of the hypothalamic and midbrain defence areas ranged from 1.5 to 44 ms and 2 to 60 ms respectively. There was no statistical difference between two groups. Excitation followed by inhibition or inhibition followed by excitation was observed in these processes. Excitatory post-synaptic potentials (EPSPs) were summated by simultaneous stimulation of both sites and the onset latency was changed with the change of stimulus intensity. It is concluded that projections from the defence areas of hypothalamus and midbrain are relayed to RVLM neurones forming excitatory and inhibitory synapses; one mechanism of the effect summation caused by both sites is via EPSPs.