Cx26 regulates proliferation of repairing basal airway epithelial cells.

The recovery of an intact epithelium following injury is critical for restoration of lung homeostasis, a process that may be altered in cystic fibrosis (CF). In response to injury, progenitor cells in the undamaged areas migrate, proliferate and re-differentiate to regenerate an intact airway epithelium. The mechanisms regulating this regenerative response are, however, not well understood. In a model of circular wound injury of well-differentiated human airway epithelial cell (HAEC) cultures, we identified the gap junction protein Cx26 as an important regulator of cell proliferation. We report that induction of Cx26 in repairing HAECs is associated with cell proliferation. We also show that Cx26 is expressed in a population of CK14-positive basal-like cells. Cx26 silencing in immortalized cell lines using siRNA and in primary HAECs using lentiviral-transduced shRNA enhanced Ki67-labeling index and Ki67 mRNA, indicating that Cx26 acts a negative regulator of HAEC proliferation. Cx26 silencing also markedly decreased the transcription of KLF4 in immortalized HAECs. We further show that CF HAECs exhibited deregulated expression of KLF4, Ki67 and Cx26 as well enhanced rate of wound closure in the early response to injury. These results point to an altered repair process of CF HAECs characterized by rapid but desynchronized initiation of HAEC activation and proliferation.

What does the future hold for diabetic dyslipidaemia?

Preliminary evidence from trials with the HMG-CoA reductase inhibitors (statins), simvastatin and pravastatin, suggests that aggressive treatment of diabetic dyslipidaemia will reduce coronary events. Questions regarding the prevention of cardiovascular events in diabetic patients are now being addressed in prospectively designed trials. The first question is, can aggressive treatment of dyslipidaemia lead to primary prevention of cardiovascular events in patients with type 2 diabetes? This is being addressed in the ongoing Atorvastatin Study for the Prevention of coronary heart disease Endpoints in NIDDM (ASPEN) and the Collaborative AtoRvastatin Diabetes Study (CARDS). These trials will randomize over 4000 patients with type 2 diabetes and no previous myocardial infarction to either atorvastatin or placebo for 4 years. The second question is, are there benefits for aggressive lipid lowering to levels below those recommended in current treatment guidelines, i.e. is lower better? Results from the recent Atorvastatin VErsus Revascularization Treatment (AVERT) trial suggest this to be the case. AVERT showed that, in stable coronary heart disease patients who had been referred for revascularization, aggressive lowering of low density lipoprotein (LDL) cholesterol with atorvastatin 80 mg/day (to a mean level of 2.0 mmol/L [77 mg/dL]) reduced the incidence of ischaemic events by 36% compared with angioplasty and usual care (which reduced LDL cholesterol to 3.1 mmol/L [119 mg/dL]). The 36% reduction in events with atorvastatin versus angioplasty and usual care trended towards significance (p=0.048). The benefits of aggressive lipid-lowering therapy are also being investigated in the ongoing Treating to New Targets (TNT) and Incremental Decrease in Endpoints through Aggressive Lipid lowering (IDEAL) trials. These studies will more closely examine the benefits of treating diabetic dyslipidaemia, and will determine how aggressively this abnormal lipid profile should be treated.

Adipose cell morphology and control of lipolysis in a patient with partial lipodystrophy.

A previously unreported patient with partial (cephalothoracic) lipodystrophy is described. Glucose tolerance and plasma lipids were normal, but plasma insulin increased to 340 muU/ml during an oral glucose tolerance test. Plasma free fatty acids were appropriately suppressed by oral glucose, insulin, and nicotinic acid, and were increased by infusion of norepinephrine. The lipolytic responses was also normal in response to two stimuli for endogenous catecholamine release: upright posture and 2-deoxyglucose infusion. There was a gradual development of postural hypotension in response to upright posture despite appropriate reflex tachycardia. Anhidrosis was present over the lower half of the body during this test, in a distribution corresponding to the area of adipose tissue hypertrophy. Anhidrosis was also seen in this region in response to warm ambient temperature. Adipose cells from the atrophic area were smaller than those from the hypertropic area, but the atrophic cells were only 65% of the volume of the hypertrophic cells by two different methods. Thus, loss of cells occurred. Glucose-1(-14)C utilization and in vitro lipolysis were similar in the two cell preparations; the difference were explicable by cell size and did not suggest a metabolic abnormality. Counts of unmyelinated nerves were similar in the two areas. These findings indicate that in this patient the lipodystrophy was associated with normal fat cells and an autonomic dysfunction. However, the findings cannot completely explain the pathogenesis of her disorder. Loss of fat cells, rather than symmetrical shrinkage, occurred in the upper half of the body.

Incorporation of 75Se-selenomethionine into human apoproteins. III. Kinetic behavior of isotopically labeled plasma apoprotein in man.

The metabolism of lipoprotein-apoprotein was examined in four subjects with normal lipid metabolism and in one subject with type II hyperlipemia by means of isotopic tracer methodology. Studies were performed after intravenous injection of a radioactive amino acid precursor for apoprotein synthesis (75Se-selenomethionine), in both the basal state and following the acute injection of intravenous heparin. Computer technics were used to evaluate a series of multicompartmental models, and a general model is proposed that yields optimum fitting of experimental data for serum free amino acid precursor, very-low-density lipoprotein-apoprotein (VLD-apoprotein), and low-density lipoprotein-apoprotein (LDL-apoprotein) in man. The analysis demonstrates that approximately half of the transport of 75Se-apoVLDL from the plasma VLDL pool is converted to 75Se-apoLDL. The acute injection of heparin in two normal subjects results in a two-and-a-half-fold increase in this rate of conversion of 75Se-apoVLDL to 75Se-apoLDL. 75Se-apoLDL is metabolized by rapid transport into a recycling extravascular pool and by irreversible catabolism. The fractional rate of recycling is large relative to the fractional rate of catabolism of apoLDL (3.7:1.0), suggesting extravascular recycling as a potential site of regulation of the plasma concentration of apoLDL. In a patient with type II hyperlipemia, the extravascular recycling pathway is reduced and is not corrected with D-thyroxine therapy. However, this therapy did reduce conversion of apoVLDL to apoLDL in this type II patient. The kinetic data support the validity of the compartmental model in simulating both normal and pathologic apoprotein metabolism and that perturbation of physiology seen with heparin injection and D-thyroxine therapy. These data support a quantitative role of apoVLDL as a precursor of apoLDL and identify an important recycling pathway of apoLDL metabolism in addition to that of catabolism.

Incorporation of 75Se-selenomethionine into human apoproteins. II. Characterization of metabolism of very-low-density and low-density lipoproteins in vivo and in vitro.

This investigation is designed to explore the potential role of apo VLDL as a precursor of a polypeptide component of human LDL. Attention was directed to the chromatography-defined Sf-I polypeptide fraction of apo VLDL, which has been previously shown to be immunologically and chemically indistinguishable from the major component of apoLDL.1-3 In VLDL isolated from bloow drawn within two hours following 75Se-SM injection, the Sf-I polypeptide fraction of apo VLDL was highly enriched with isotope, providing an appropriate preparation for in-vitro tracer studies. Conversion of 75Se-VLDL to 75Se-LDL occurred in vitro in the presence of normal plasma at 37 degrees C., and this conversion was augmented by post-heparin plasma. No conversion to HDL lipoproteins could be detected. Injection of heparin in vivo resulted in acute reciprocal changes in the radioactivity contained within serum apo VLDL and apoLDL. These findings suggest that a component of the Sf-I polypeptide fraction of apo VLDL can be metabolized into the apoprotein of LDL in man. Thus, the biochemical and immunologic similarities between the Sf-I fractions of apoVLDL and apoLDL may result from a physiologic "precursor-product" relationship between the apoprotein moieties of these two lipoprotein species. A method for further investigation of the metabolism of human apoprotein is suggested.

Stimulation of insulin secretion by long-chain free fatty acids. A direct pancreatic effect.

A continuous-flow centrifuge was used to infuse sodium salts of oleic, linoleic, lauric, or palmitic acid into the pancreatic artery of anesthetized dogs. In these regional perfusion studies there was no increase in FFA levels in the general circulation. Elevation of pancreatic FFA levels produced an immediate increase in pancreatic venous immunoreactive insulin (IRI). After 10 min of FFA infusion. IRI levels declined somewhat from the initial peak response but soon rose again to high levels which were then sustained until the infusion was terminated. All four long-chain FFA tested produced a similar biphasic IRI response. Clearcut increases in IRI were associated with absolute FFA levels (measured in pancreaticoduodenal venous plasma) as low as 0.6-0.8 mueq/ml and with increments over basal levels of as little as 0.4-0.5 mueq/ml. At higher levels of FFA, absolute IRI levels in the pancreatic venous effluent exceeded 1,000 muU/ml in some experiments and 5- to 10-fold increases over basal values were observed. These studies indicate that long-chain FFA, in physiological concentrations, can markedly stimulate insulin secretion by a direct effect on the pancreas. The results lend support to the concept of insulin as a hormone that is importantly involved in regulating the metabolism of all three principal classes of metabolic substrates and whose release is in turn regulated by all of them. The relative importance and precise nature of its physiologic role in the regulation of lipolysis, lipid deposition, and ketone body formation remains to be established.

Infusion of long-chain fatty acid anions by continuous-flow centrifugation.

We have developed a method for the rapid infusion into plasma of large amounts of long-chain free fatty acids (FFA). Unanesthetized dogs were connected by a peripheral artery to a closed, continuousflow centrifuge from which cells and plasma emerged in separate lines. Sodium oleate was infused directly into the plasma line before cells and plasma were recombined and returned to the animal through a peripheral vein.The centrifugation procedure itself produced only small changes in circulating levels of glucose, FFA, and electrolytes. Plasma flow rates as high as 100 ml/min could be maintained, and centrifugations of 12 hr were accomplished without complications. During centrifugation, sodium oleate was infused at rates up to 80 muEq/kg per min for 2.5 hr; the maximum molar ratio of FFA to albumin without hemolysis was 10:1. Plasma FFA levels rose rapidly after infusions were started and reached constant elevated levels within 15-20 min. Oleate infusion at 10-50 muEq/kg per min produced a rise in plasma FFA proportional to the infusion rate. The maximum increment in plasma FFA above control values was 1.66 muEq/ml. When infusions ended, plasma FFA declined rapidly to control levels. Oleate infusion at rates below 30 muEq/kg per min did not reduce levels of other plasma FFA. Infusion at high rates was accompanied by a marked fall in blood glucose. This method permits adminsitration of long-chain fatty acids in sufficient quantities to study their individual metabolic effects, and provides a new way to supply lipid calories parenterally.

Stimulation of insulin secretion by infusion of free fatty acids.

The acute elevation of plasma free fatty acid (FFA) levels by direct infusion of sodium oleate into the plasma of conscious dogs was accompanied by the rapid onset of a 2- to 12-fold increase in plasma immunoreactive insulin, and, subsequently, a marked fall in plasma glucose, even in dogs receiving intravenous glucose throughout the infusion. The magnitude of both the insulin and glucose responses correlated with the mean FFA level during infusion. A large increase in plasma insulin and fall in glucose also occurred when glycerol was infused with oleate in order to simulate endogenous lipolysis more closely. Insulin levels in pancreaticoduodenal vein blood rose markedly during oleate infusion, while plasma ketone levels rose only slightly. In contrast to the effects of oleate infusion, elevation of plasma FFA to correspondingly high levels by triolein ingestion and intravenous heparin produced only small increases in plasma insulin, which did not correlate well with the FFA level reached, and small increases in plasma glucose.The results indicate that under certain conditions elevated FFA levels may be a potent stimulus of insulin secretion. This response is modified under other conditions such as during chylomicron removal under the influence of heparin. This effect may play a role in the regulation of lipolysis and ketone formation, but determination of the exact mechanism of FFA stimulation of the pancreas and its physiological significance will require further investigation.