Onset and rate of striatal atrophy in preclinical Huntington disease

BACKGROUND

Huntington disease (HD) is characterized by striatal atrophy that begins long before the onset of motor symptoms.

OBJECTIVE

To determine when striatal atrophy begins, the extent and rate of atrophy before diagnosis of motor symptoms, and whether striatal atrophy can predict when symptom onset will occur.

METHODS

Caudate and putamen volumes were measured on MRI scans of 19 preclinical subjects with the HD gene expansion who were very far (9 to 20 years) from estimated onset, and on serial scans from 17 preclinical subjects, six of whom were diagnosed with HD within 5 years after the initial scan.

RESULTS

Striatal volumes were significantly smaller for the subjects who were very far from estimated onset than for age-matched control subjects. Statistical models fit to the longitudinal data suggest that rate of caudate atrophy becomes significant when subjects are approximately 11 years from estimated onset and rate of putamen atrophy becomes significant approximately 9 years prior to onset. In the six incident cases, caudate and putamen were approximately one-third to one-half of normal volume at diagnosis, and caudate volume alone was able to predict with 100% accuracy those subjects who would be diagnosed within 2 years of imaging.

CONCLUSIONS

Striatal atrophy begins many years prior to diagnosable HD, and assessment of atrophy on MRI may be very useful in both predicting HD onset and in tracking progression in future therapeutic trials in preclinical subjects.

Runners adjust leg stiffness for their first step on a new running surface

Human runners adjust the stiffness of their stance leg to accommodate surface stiffness during steady state running. This adjustment allows runners to maintain similar center of mass movement (e.g., ground contact time and stride frequency) regardless of surface stiffness. When runners encounter abrupt transitions in the running surface, they must either make a rapid adjustment or allow the change in the surface stiffness to disrupt their running mechanics. Our goal was to determine how quickly runners adjust leg stiffness when they encounter an abrupt but expected change in surface stiffness that they have encountered previously. Six human subjects ran at 3 m s(-1) on a rubber track with two types of rubber surfaces: a compliant "soft" surface (ksurf = 21.3 kN m(-1) and a non-compliant "hard" surface (ksurf = 533 kN m(-1). We found that runners completely adjusted leg stiffness for their first step on the new surface after the transition. For example, runners decreased leg stiffness by 29% between the last step on the soft surface and the first step on the hard surface (from 10.7 kN m(-1) to 7.6 kN m(-1), respectively). As a result, the vertical displacement of the center of mass during stance ( approximately 7 cm) did not change at the transition despite a reduction in surface compression from 6 cm to less than 0.25 cm. By rapidly adjusting leg stiffness, each runner made a smooth transition between surfaces so that the path of the center of mass was unaffected by the change in surface stiffness.

Increased nitric oxide inactivation by reactive oxygen species in lead-induced hypertension

BACKGROUND

We have recently found evidence for increased reactive oxygen species (ROS) in rats with lead-induced hypertension. We hypothesized that increased ROS activity may contribute to hypertension by enhancing inactivation of nitric oxide (NO) in this model.

METHODS

Rats were treated for 12 weeks with either lead acetate (100 p.p.m.) alone (Pb group) or lead acetate plus vitamin E-fortified food (5000 U/kg rat chow, Pb + E group). The control animals were fed either regular rat chow or a vitamin E-fortified diet. Blood pressure, creatinine clearance, and urinary excretion of stable NO metabolites (NOx) were monitored, and plasma and tissue abundance of nitrotyrosine, which is the footprint of NO oxidation by ROS, were determined.

RESULTS

The Pb group showed a marked rise in blood pressure, a significant increase in plasma and kidney, heart, liver, and brain nitrotyrosine abundance, and a substantial fall in urinary NOx excretion. Concomitant administration of high-dose vitamin E in the Pb + E group ameliorated hypertension and normalized both urinary NOx excretion and tissue nitrotyrosine without altering tissue lead content. However, vitamin E supplementation had no discernible effect on either blood pressure or nitrotyrosine abundance in the normal controls.

CONCLUSIONS

These findings point to enhanced ROS-mediated inactivation and sequestration of NO, which can potentially contribute to hypertension, tissue damage, and reduced urinary NOx excretion in rats with lead-induced hypertension. The beneficial effects of high-dose vitamin E on blood pressure, tissue nitrotyrosine burden, and urinary NOx excretion support the role of increased ROS activity in the pathogenesis of these abnormalities in this model.

Down-regulation of hepatic lecithin:cholesterol acyltransferase gene expression in chronic renal failure

BACKGROUND

Chronic renal failure (CRF) is associated with premature arteriosclerosis, impaired high-density lipoprotein (HDL) maturation, increased pre-beta HDL (a lipid-poor HDL species), reduced HDL/total cholesterol ratio, hypertriglyceridemia, and depressed lipolytic activity. The latter has been, in part, attributed to elevated pre-beta HDL, which is a potent inhibitor of lipoprotein lipase (LPL). Accumulation of cholesterol in the arterial wall is a critical step in atherogenesis, and HDL-mediated cholesterol removal from peripheral tissues mitigates atherosclerosis. Lecithin:cholesterol acyltransferase (LCAT) is essential for maturation of HDL and cholesterol removal by HDL from peripheral tissues. Earlier studies have revealed depressed plasma LCAT enzymatic activity in patients with CRF. This study was conducted to determine whether impaired LCAT activity can be confirmed in CRF animals and if so whether it is due to down-regulation of hepatic LCAT expression.

METHODS

Hepatic tissue LCAT mRNA and plasma LCAT enzymatic activity were measured in male Sprague-Dawley rats six weeks after excisional 5/6 nephrectomy or sham operation.

RESULTS

Compared with the controls, the CRF group exhibited a significant reduction of hepatic tissue LCAT mRNA abundance. The reduction in hepatic LCAT mRNA was accompanied by a marked reduction of plasma LCAT activity and elevation of serum-free cholesterol in the CRF animals. LCAT activity correlated positively with the HDL/total cholesterol ratio and inversely with free cholesterol and triglyceride concentrations.

CONCLUSIONS

CRF leads to a marked down-regulation of hepatic LCAT mRNA expression and plasma LCAT activity. This abnormality can impair HDL-mediated cholesterol uptake from the vascular tissue and contribute to cardiovascular disease. In addition, LCAT deficiency can, in part, account for elevated serum-free cholesterol, reduced HDL/total cholesterol, and elevated pre-beta HDL in CRF. The latter can, in turn, depress lipolytic activity and hinder triglyceride-rich lipoprotein clearance in CRF.

Roles of the PI-3K and MEK pathways in Ras-mediated chemoresistance in breast cancer cells

Activated Ras utilises several downstream pathways, including the mitogen-activated protein kinase (MAPK) kinase (MEK)/MAPK pathway and the phosphoinositide 3-kinase (PI-3k)/Akt pathway, to promote cell proliferation and to inhibit apoptosis. To investigate which pathway plays a major role in Ras-induced drug resistance to chemotherapeutic agents in breast cancer cells, we transfected MCF7 breast cancer cells with a constitutively active H-RasG12V and examined the toxicities of three commonly used breast cancer chemotherapeutic agents, paclitaxel, doxorubicin, and 5-fluorouracil in these cells under the conditions that PI-3K or MEK were selectively inhibited by their respective specific inhibitors or dominant negative expression vectors. We found that Ras-mediated drug resistance is well correlated with resistance to apoptosis induced by anticancer agents in MCF7 breast cancer cells. Although inhibition of MEK/MAPK or PI-3K/Akt can each enhance the cytotoxicity of paclitaxel, doxorubicin, or 5-fluorouracil, inhibition of the PI-3K/Akt pathway seems to have a greater effect than inhibition of the MEK/MAPK pathway in reversing Ras-mediated drug resistance. Our results indicate that the PI-3K pathway may play a more important role in receptor tyrosine kinase-mediated resistance to chemotherapy and suggest that PI-3K/Akt might be a critical target molecule for anticancer intervention in breast cancer.

Feasibility of tuberculosis treatment monitoring by video directly observed therapy: a binational pilot study

BACKGROUND

Although directly observed therapy (DOT) is recommended worldwide for monitoring anti-tuberculosis treatment, transportation and personnel requirements limit its use.

OBJECTIVE

To evaluate the feasibility and acceptability of 'video DOT' (VDOT), which allows patients to record and transmit medication ingestion via videos watched remotely by health care providers to document adherence.

METHODS

We conducted a single-arm trial among tuberculosis (TB) patients in San Diego, California, USA, (n = 43) and Tijuana, Mexico (n = 9) to represent high- and low-resource settings. Pre-/post-treatment interviews assessed participant characteristics and experiences. Adherence was defined as the proportion of observed doses to expected doses.

RESULTS

The mean age was 37 years (range 18-86), 50% were male, and 88% were non-Caucasian. The mean duration of VDOT use was 5.5 months (range 1-11). Adherence was similar in San Diego (93%) and Tijuana (96%). Compared to time on in-person DOT, 92% preferred VDOT, 81% thought VDOT was more confidential, 89% never/rarely had problems recording videos, and 100% would recommend VDOT to others. Seven (13%) participants were returned to in-person DOT and six (12%) additional participants had their phones lost, broken or stolen.

CONCLUSIONS

VDOT was feasible and acceptable, with high adherence in both high- and low-resource settings. Efficacy and cost-effectiveness studies are needed.

Spectral integration in primary auditory cortex: Laminar processing of afferent input, in vivo and in vitro

Auditory cortex neurons integrate information over a broad range of sound frequencies, yet it is not known how such integration is accomplished at the cellular or systems levels. Whereas information about frequencies near a neuron's characteristic frequency is likely to be relayed to the neuron by lemniscal thalamocortical inputs from the ventral division of the medial geniculate nucleus, we recently proposed that information about frequencies spectrally distant from characteristic frequency is mainly relayed to the neuron via "horizontal" intracortical projections from neurons with spectrally-distant characteristic frequencies [J Neurophysiol 91 (2004) 2551]. Here we test this hypothesis by using current source density analysis to determine if characteristic frequency and spectrally-distant non-characteristic frequency stimuli preferentially activate thalamocortical and horizontal pathways, respectively, in rat auditory cortex. Characteristic frequency stimuli produced current source density profiles with prominent initial current sinks in layers 3 and 4--the termination zone of lemniscal inputs from medial geniculate nucleus. In contrast, stimuli three octaves below characteristic frequency produced initial current sinks mainly in the infragranular layers. Differences between current source density profiles were only apparent for initial current sinks; profiles for longer-latency current sinks evoked by characteristic frequency and non-characteristic frequency stimuli overlapped to a greater degree, likely due to shared mechanisms of intracortical processing or to longer-latency thalamocortical contributions (lemniscal and nonlemniscal). To identify current source density profiles produced by activation of lemniscal thalamocortical inputs alone, we utilized the mouse auditory thalamocortical slice preparation. Electrical stimulation of the medial geniculate nucleus in vitro produced major current sinks in cortical layers 3/4, and excitation spread horizontally from this point throughout primary auditory cortex to produce current sinks in multiple cortical layers. These data support the hypothesis that relay of thalamocortical information throughout auditory cortex via horizontal intracortical projections may be the basis of broad spectral integration in vivo.

Down-regulation of tissue lipoprotein lipase expression in experimental chronic renal failure

Chronic renal failure (CRF) is associated with hypertriglyceridemia, impaired clearance of very low density lipoproteins (VLDL) and chylomicrons and their remnants as well as triglyceride-enrichment of various lipoproteins. These abnormalities are indicative of depressed lipoprotein lipase (LPL)-mediated hydrolysis of triglycerides in VLD and chylomicrons. In fact, impaired post-heparin lipolytic activity and decreased adipose tissue LPL activity has been previously demonstrated in CRF. The reduction in LPL activity in CRF has been attributed to PTH-induced insulin resistance and the presence of excess lipase inhibitors in uremic plasma. However, the effect of CRF on gene expression of LPL has not been elucidated and was studied here. Heparin-releasable, detergent-extractable and total LPL activities, as well as LPL mRNA of the heart, soleus muscle and fat body were determined in male Sprague-Dawley rats at baseline and on weeks 1, 3 and 6 following 5/6 nephrectomy (CRF group) or sham operation (control group). The CRF group exhibited a marked and steady rise in plasma triglycerides along with a steady decline in LPL activities and mRNA levels of all tissues studied. In contrast, the study parameters remained virtually unchanged throughout the study period in the control group. A strong inverse correlation was found between plasma triglycerides and LPL activity in the study animals. LPL activity was directly related to LPL mRNA. We conclude that CRF results in marked down-regulation of LPL expression that can contribute to dyslipidemia and altered energy metabolism in uremia. The effect of depressed LPL expression is compounded by the previously demonstrated elevations in uremic plasma of Apo C-III and pre-beta-HDL, which are potent inhibitors of LPL.

Hepatic HDL receptor, SR-B1 and Apo A-I expression in chronic renal failure

BACKGROUND

Chronic renal failure (CRF) is associated with hypertriglyceridaemia and depressed plasma high-density lipoprotein (HDL)-cholesterol and apolipoprotein A-I (Apo A-I) concentrations. Uraemic hypertriglyceridaemia is due, in part, to lipoprotein lipase and hepatic lipase deficiencies, which are causally linked to excess parathormone (PTH). This study was designed to test the hypothesis that depressed plasma concentration and abnormal composition of HDL in CRF may be due to dysregulation of hepatic expression of Apo A-I and/or the newly discovered HDL receptor.

METHODS

Hepatic Apo A-I and HDL receptor mRNA abundance (Northern blot), and HDL receptor protein mass (Western blot) were determined in CRF rats (5/6 nephrectomy), parathyroidectomized CRF rats (CRF-PTx) and sham-operated controls.

RESULTS

The CRF group exhibited normal hepatic HDL receptor mRNA and HDL receptor protein abundance coupled with reduced hepatic Apo A-I mRNA. Hepatic Apo A-I mRNA, HDL receptor mRNA and protein abundance were not affected by PTx.

CONCLUSIONS

CRF results in the down-regulation of hepatic Apo A-I gene expression, which accounts for the known reduction in plasma Apo A-I concentration. However, CRF does not affect HDL receptor mRNA or protein expression in this model. Neither Apo A-I nor HDL receptor expression were modified by PTx in CRF rats.

Down-regulation of VLDL receptor expression in chronic experimental renal failure

VLDL receptor (VLDL-R) is a novel member of the LDL receptor gene family with distinct tissue distribution and function. It binds and internalizes VLDL particles and is primarily expressed in skeletal muscle, heart, brain and adipose tissue, which use fatty acids for energy production or storage. CRF is associated with elevated serum triglyceride and VLDL concentrations and depressed VLDL and chylomicron clearance. We have recently shown marked down-regulation of lipoprotein lipase expression in CRF. This study was conducted to test the hypothesis that VLDL-R expression may be similarly depressed in CRF. To this end, VLDL-R mRNA (Northern blot) and protein mass (Western blot) of skeletal muscle (soleus) and heart were measured in male Sprague-Dawley rats six weeks after 5/6 nephrectomy (CRF group) or sham operation (NL group). A group of erythropoietin (EPO)-treated (150 U/kg twice weekly) CRF animals was included to determine the possible effect of EPO-deficiency anemia (EPO-CRF group). Subgroups of animals were studied at weeks 1, 3 and 6. The CRF group showed a fivefold increase in plasma triglyceride concentration. This was associated with an impressive fourfold reduction in heart and skeletal muscle VLDL-R mRNA and protein mass. VLDL-R mRNA levels in the heart and skeletal muscle were directly related to creatinine clearance and inversely related to serum triglyceride and VLDL concentrations. EPO therapy led to a mild improvement in CRF hypertriglyceridemia but failed to improve VLDL-R expression. Thus, the rise in plasma triglyceride and VLDL concentrations in CRF animals was associated with marked down-regulation of VLDL-R expression. Down-regulation of VLDL-R expression, shown here for the first time, reveals another facet of disturbed lipid metabolism in CRF.

Acquired lecithin-cholesterol acyltransferase deficiency in nephrotic syndrome

Lecithin-cholesterol acetyltransferase (LCAT) is involved in the synthesis of plasma cholesteryl esters and is pivotal in the maturation of plasma high-density lipoprotein (HDL) and conversion of HDL3 to HDL2. In nephrotic syndrome (NS), the ratio of HDL2 to HDL3 is low even though the total concentration of HDL is generally normal. We hypothesize that the reduced HDL2/HDL3 ratio in NS is due to urinary losses of LCAT, leading to plasma LCAT deficiency. To test this hypothesis, Sprague-Dawley rats were randomized to NS (given 130 mg puromycin aminonucleoside on day 1 and 60 mg ip on day 14) or control groups and were studied on day 30. To dissect the effect of proteinuria from hypoalbuminemia, a group of Nagase rats with inherited hypoalbuminemia was included. Hepatic LCAT and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA abundance and plasma and urine LCAT activity were measured. The NS group showed a fourfold rise in serum cholesterol and triglycerides, a fivefold rise in free cholesterol, and a fourfold fall in the HDL-to-total cholesterol ratio. Despite severe hypoalbuminemia, the Nagase rats showed only a mild elevation of serum cholesterol and triglycerides with a normal serum free cholesterol and HDL-to-total cholesterol ratio. The NS group exhibited a normal hepatic LCAT-to-GAPDH mRNA ratio, a marked reduction in plasma LCAT activity, and a significant increase in urinary LCAT excretion. LCAT/GAPDH mRNA and plasma and urine LCAT were normal in Nagase rats. Thus NS led to heavy urinary losses and reduced plasma concentration of LCAT, despite normal hepatic LCAT mRNA abundance. However, hypoalbuminemia, per se, without proteinuria as seen in the Nagase rats had no effect on plasma LCAT or the HDL-to-total cholesterol ratio. Therefore, proteinuria, not hypoalbuminemia, causes LCAT deficiency and a depressed HDL-to-total cholesterol ratio in NS.

Down-regulation of hepatic high-density lipoprotein receptor, SR-B1, in nephrotic syndrome

BACKGROUND

Nephrotic syndrome (NS) is a prototype of acquired hypercholesterolemia. Hepatic synthesis and removal of cholesterol play major roles in the regulation of plasma concentration of this sterol. Low-density lipoprotein (LDL) and high-density lipoprotein (HDL) particles are the primary vehicles for cholesterol transport to the liver. We have recently demonstrated that NS results in acquired hepatic LDL receptor deficiency in rats. This study was undertaken to determine the effect of NS on hepatic expression of the newly discovered, long-sought HDL receptor.

METHODS

Hepatic HDL receptor and apolipoprotein A-I (apo A-I) expressions were studied in rats with puromycin-induced NS. The results were compared with those obtained in placebo-treated, normal controls.

RESULTS

The NS group exhibited a marked reduction in hepatic tissue HDL receptor protein abundance when compared with the control group. In contrast, hepatic HDL receptor mRNA abundance in the NS group was similar to that of the control group. As expected, the NS group showed a marked increase in hepatic apo A-I mRNA abundance.

CONCLUSIONS

The study explored the effect of experimental NS on hepatic HDL receptor expression, and the results revealed a marked down-regulation of HDL receptor in rats with NS. In contrast, hepatic expression of Apo A-I, the principal protein constituent of HDL, was markedly increased in NS rats. The HDL receptor deficiency shown here can potentially limit the efficiency of HDL as the primary vehicle for reverse cholesterol transport in NS.

Enhancement of antitumor activity of the anti-EGF receptor monoclonal antibody cetuximab/C225 by perifosine in PTEN-deficient cancer cells

Mutational inactivation or deletion of the phosphatase and tensin homologue deleted on chromosome 10 (PTEN)/MMAC1/TEP gene in human cancer cells leads to a constitutively active status of the phosphatidylinositol 3-kinase/Akt pathway in the cells and has been linked to the lack of responses of the cells to the epidermal growth factor (EGF) receptor-targeted therapeutics. Akt is strongly inhibited by perifosine, an orally active alkyl-lysophospholipid currently being evaluated as an anti-cancer agent in phase 1 and 2 clinical trials. To determine whether perifosine may enhance the antitumor activity of the anti-EGF receptor monoclonal antibody cetuximab/C225 in PTEN-deficient cancer cells, we exposed MDA468 breast cancer cells (which contain mutated PTEN gene) and PC3 prostate cancer cells (in which the PTEN gene is deleted) to perifosine and cetuximab, alone and in combination. Treatment of the cells with perifosine reduced baseline levels of phosphorylated Akt, phosphorylated p44/42 mitogen-activated protein kinase (MAPK) and p38MAPK, and increased baseline levels of phosphorylated stress-activated protein kinase (SAPK)/c-jun NH(2)-terminal kinase (JNK). A 72-h exposure of the MDA468 and PC3 cells to perifosine alone resulted in cell death in a dose-dependent manner, which was enhanced by cetuximab. Addition of subtoxic doses of perifosine to cetuximab treatment also enhanced the cetuximab-induced growth inhibition. The combination treatment enhanced the inhibition of phosphorylation of Akt, p44/42MAPK and p38MAPK, but offset the phosphorylation of SAPK/JNK that was activated by perifosine treatment alone. Taken together, the data showed that perifosine enhances the antitumor activity of cetuximab in PTEN-deficient cancer cells. Further evaluation of the combination treatment in preclinical and clinical studies is warranted.

Lead-induced hypertension. III. Increased hydroxyl radical production

Lead-induced hypertension has previously been shown to be closely associated with an increase in reactive oxygen species in low lead (100 ppm)-treated rats. The present study has attempted to define the specific moiety involved by noting the blood pressure (BP), reactive oxygen species (MDA-TBA), hydroxyl radical, and nitrotyrosine responses to infusion of the reactive oxygen species scavenger dimethylthiourea. Dimethylthiourea, a reputed scavenger of hydroxyl radical, normalized BP and MDA-TBA in the lead-treated rats but had no effect in normal control animals. MDA-TBA, hydroxyl radical, and nitrotyrosine, the tissue end product of peroxynitrite, were reduced to or toward normal by dimethylthiourea. The results, therefore, are consistent with the suggestion that either hydroxyl radical or peroxynitrite may be the reactive species affected by lead.

Down-regulation of hepatic lipase expression in experimental nephrotic syndrome

Hepatic lipase (HL) plays an important role in catabolism of chylomicron remnants, conversion of intermediate density lipoprotein (IDL) to low-density lipoprotein (LDL) and reverse transport of cholesterol to the liver. Several features of the nephrotic dyslipidemia point to the possible presence of HL deficiency. In an attempt to address this possibility, gene expression of HL was studied in rats with puromycin-induced nephrotic syndrome (NS). The results were compared with those obtained in a group of placebo-treated control animals. The NS group showed marked proteinuria, hypoalbuminemia, hypercholesterolemia, hypertriglyceridemia, normal creatinine clearance and normal hepatic tissue cholesterol concentration. HL activity of the liver tissue was reduced by approximately 60% in the NS group as compared to that found in the normal control group. The reduction of HL activity in the NS group was accompanied by a reduction of HL mRNA of virtually similar magnitude. HL activity of the liver tissue was inversely related to urinary protein excretion, serum cholesterol and serum triglyceride concentrations. In contrast, HL activity was directly related to serum albumin concentration and HL mRNA. No significant difference was observed in HL activity between the control group and the pre-nephrotic animals studied at days 1 and 5 following puromycin administration. This observation excludes an acute effect of puromycin as a possible cause of HL deficiency in the NS animals. Thus, NS in this model results in a marked down-regulation of HL expression which may, in part, contribute to the nephrotic dyslipidemia.

A freestanding NiSxporous film as a binder-free electrode for Mg-ion batteries

A freestanding NiS_xporous film delivers high volumetric Mg-ion storage capacity.

Acquired VLDL receptor deficiency in experimental nephrosis

Nephrotic syndrome (NS) is commonly associated with elevation of plasma very low density lipoprotein (VLDL) and triglyceride concentrations. VLDL receptor (VLDL-R) is a novel protein that specifically binds and internalizes VLDL particles and is primarily distributed in heart, skeletal muscle, brain and adipose tissue. Based on these properties, VLDL-R is thought to play a role in VLDL and triglyceride metabolism. The present study was undertaken to test the hypothesis that elevation of plasma VLDL in NS may be, in part, related to VLDL-R deficiency. To this end, heart and skeletal muscle VLDL-R protein (Western blot) and mRNA (Northern blot) were measured at various points in the course of puromycin-induced NS in rats. The results were compared with those obtained in the placebo-treated normal control animals. The NS group showed a significant decline in VLDL-R protein (relative to total plasma membrane protein mass) in the heart and skeletal muscle paralleling the rise in plasma VLDL and triglyceride concentrations. The fall in VLDL-R protein was accompanied by a parallel decline in VLDL-R mRNA in the heart but not skeletal muscle. VLDL-R protein was directly related to proteinuria and inversely related to plasma VLDL and triglyceride concentrations. In conclusion, puromycin-induced NS in rats is associated with profound reduction in heart and skeletal muscle VLDL receptor protein. Acquired VLDL-R deficiency, shown for the first time here, may contribute to elevation of plasma concentration of triglyceride-rich VLDL in the nephrotic rat. Recognition of this abnormality reveals another dimension of the complex dysregulation of lipid metabolism in NS. The precise mechanism responsible for NS-induced VLDL-R deficiency in this model is not clear and awaits further investigation.

Role of secondary hyperparathyroidism in the genesis of hypertriglyceridemia and VLDL receptor deficiency in chronic renal failure

Recent studies have revealed marked down-regulation of hepatic lipase (HL), lipoprotein lipase (LPL) and very low density lipoprotein-receptor (VLDL-R) expressions in animals with chronic renal failure (CRF). Acquired deficiency of these proteins, which together play an important role in catabolism of triglyceride-rich lipoproteins, is involved in the pathogenesis of CRF hypertriglyceridemia. Down-regulation of HL and LPL expressions in CRF can be completely reversed by parathyroidectomy (PTx), suggesting the role of excess parathormone (PTH). However, the role of hyperparathyroidism in the pathogenesis of CRF-induced VLDL-R deficiency has not been investigated before, and was studied here. To this end, VLDL-R mRNA (Northern analysis) and VLDL-R protein (Western analysis) of the fat pad and soleus muscle were compared in CRF (5/6 nephrectomized) rats, CRF animals with PTx (CRF-PTx) and sham-operated control animals. The CRF animals exhibited marked hypertriglyceridemia coupled with significant reductions in skeletal muscle and adipose tissue VLDL-R mRNA abundance and protein mass. Parathyroidectomy resulted in a significant, but partial, amelioration of CRF hypertriglyceridemia. However, in contrast to its effect on HL and LPL expressions, PTx did not improve VLDL-R expression, suggesting a PTH-independent mechanism for the latter abnormality. The differential effect of PTx on HL and LPL on the one hand and VLDL-R on the other can, in part, account for partial as opposed to complete correction of the associated hypertriglyceridemia with PTx in the CRF animals.

Discovery of an orally bioavailable NK1 receptor antagonist, (2S,3S)-(2-methoxy-5-tetrazol-1-ylbenzyl)(2-phenylpiperidin-3-yl)amine (GR203040), with potent antiemetic activity

The antiemetic, pharmacokinetic, and metabolic profile of CP-99,994, a potent NK1 receptor antagonist, has been carefully evaluated. As a result we began a medicinal chemistry program which initially identified a 3-furanyl analogue (6) with improved antiemetic potency and a methyl sulfone (5) with enhanced metabolic stability and oral bioavailability. The improved pharmacokinetic profile of methyl sulfone (5) was associated with its low lipophilicity, and a therefore a number of heterocyclic analogues with reduced log D were synthesized. Out of this program emerged 19 (GR203040), a tetrazolyl-substituted analogue. Tetrazole 19 inhibits radiation-induced emesis in the ferret with high potency when administered both subcutaneously and orally, has a long duration of action, and has high oral bioavailability in the dog. Tetrazole 19 is currently undergoing evaluation as a novel approach for the control of emesis associated with, for example, cancer chemotherapy.

Secondary hyperparathyroidism downregulates lipoprotein lipase expression in chronic renal failure

In a recent study, we found marked downregulation of lipoprotein lipase (LPL) gene expression in fat, myocardium, and skeletal muscle of rats with chronic renal failure (CRF). Recently, hepatic lipase expression was shown to be depressed in CRF rats, and parathyroidectomy (PTX) was shown to reverse this abnormality. This study was undertaken to determine whether down-regulation of LPL expression in CRF is due to secondary hyperparathyroidism. Accordingly, LPL mRNA (Northern analysis), protein mass (Western analysis using mouse antibovine LPL monoclonal antibody, 5D2), and catalytic activity of the fat pad and soleus muscle were compared in five-sixths-nephrectomized male rats (CRF), parathyroidectomized CRF rats, and sham-operated control animals. The CRF animals exhibited marked hypertriglyceridemia and significant reductions of fat and skeletal muscle LPL mRNA abundance, protein mass, and catalytic activity (P < 0.05 vs. controls, for all parameters). PTX completely normalized the LPL mRNA, protein mass, and enzymatic activity and partially ameliorated the CRF hypertriglyceridemia (P < 0.05 vs. CRF group, for all parameters). Thus secondary hyperparathyroidism is responsible for impaired LPL expression in experimental CRF. This abnormality is completely corrected by PTX.

ACAT inhibition reverses LCAT deficiency and improves plasma HDL in chronic renal failure

Chronic renal failure (CRF) is associated with increased risk of arteriosclerotic cardiovascular disease and profound alteration of plasma lipid profile. Uremic dyslipidemia is marked by increased plasma concentration of ApoB-containing lipoproteins and impaired high-density lipoprotein (HDL)-mediated reverse cholesterol transport. These abnormalities are, in part, due to acquired LCAT deficiency and upregulation of hepatic acyl-CoA:cholesterol acyltransferase (ACAT). ACAT catalyzes intracellular esterification of cholesterol, thereby promoting hepatic production of ApoB-containing lipoproteins and constraining HDL-mediated cholesterol uptake in the peripheral tissues. In view of the above considerations, we tested the hypothesis that pharmacological inhibition of ACAT may ameliorate CRF-induced dyslipidemia. 5/6 Nephrectomized rats were treated with either ACAT inhibitor IC-976 (30 mg.kg(-1).day(-1)) or placebo for 6 wk. Sham-operated rats served as controls. Key cholesterol-regulating enzymes, plasma lipids, and creatinine clearance were measured. The untreated CRF rats exhibited increased plasma low-density lipoprotein (LDL) and very LDL (VLDL) cholesterol, unchanged plasma HDL cholesterol, elevated total cholesterol-to-HDL cholesterol ratio, reduced liver microsomal free cholesterol, and diminished creatinine clearance. This was accompanied by reduced plasma LCAT, increased hepatic ACAT-2 mRNA, ACAT-2 protein and ACAT activity, and unchanged hepatic HMG-CoA reductase and cholesterol 7alpha-hydroxylase. ACAT inhibitor raised plasma HDL cholesterol, lowered LDL and VLDL cholesterol, and normalized total cholesterol-to-HDL cholesterol ratio without changing total cholesterol concentration (hence, a shift from ApoB-containing lipoproteins to HDL). This was accompanied by normalizations of hepatic ACAT activity and plasma LCAT. In conclusion, inhibition of ACAT reversed LCAT deficiency and improved plasma HDL level in CRF rats. Future studies are needed to explore the efficacy of ACAT inhibition in humans with CRF.