Walter J. McConathy

Modulation of lipoprotein lipase activity by apolipoproteins. Effect of apolipoprotein C-III.

From a total of 22 hypertriglyceridemic subjects tested, 14 subjects were selected on the basis of normal postheparin plasma lipoprotein lipase (LPL) levels and the presence of LPL inhibitory activity in their fasting plasma. The inhibitory activity was detected in both the lipoprotein fraction (d less than 1.25 g/ml) and the lipoprotein-deficient fraction (d greater than 1.25 g/ml). Correlational analyses of LPL inhibitory activity and apolipoprotein levels present in the lipoprotein fraction (d less than 1.25 g/ml) indicated that only apolipoprotein C-III (ApoC-III) was significantly correlated (r = 0.602, P less than 0.05) with the inhibition activity of the lipoprotein fraction. Furthermore, it was found that LPL-inhibitory activities of the plasma lipoprotein fraction and lipoprotein-deficient fraction were also correlated (r = 0.745, P less than 0.005), though the activity in the lipoprotein-deficient plasma was not related to the ApoC-III or apolipoprotein E levels. Additional correlational analyses indicated that the LPL levels in the postheparin plasma of these subjects were inversely related to the levels of plasma apolipoproteins C-II, C-III, and E. To explain some of these observations, we directly examined the in vitro effect of ApoC-III on LPL activity. The addition of ApoC-III-2 resulted in a decreased rate of lipolysis of human very low density lipoproteins by LPL. Kinetic analyses indicated that ApoC-III-2 was a noncompetitive inhibitor of LPL suggesting a direct interaction of the inhibitor with LPL. Results of these studies suggest that ApoC-III may represent a physiologic modulator of LPL activity levels and that the incidence of LPL inhibitory activity in the plasma of hypertriglyceridemic subjects is more common than previously recognized.

Overexpression of human low density lipoprotein receptors leads to accelerated catabolism of Lp(a) lipoprotein in transgenic mice.

Lp(a) lipoprotein purified from human plasma bound with high affinity to isolated bovine LDL receptors on nitrocellulose blots and in a solid-phase assay. Lp(a) also competed with 125I-LDL for binding to human LDL receptors in intact fibroblasts. Binding led to cellular uptake of Lp(a) with subsequent stimulation of cholesterol esterification. After intravenous injection, human Lp(a) was cleared slowly from the plasma of normal mice. The clearance was markedly accelerated in transgenic mice that expressed large amounts of LDL receptors. We conclude that the covalent attachment of apo(a) to apo B-100 in Lp(a) does not interfere markedly with the ability of apo B-100 to bind to the LDL receptor and that this receptor has the potential to play a major role in clearance of Lp(a) from the circulation of intact humans.

Sudden Cardiac Death in a 20-Year-Old Bodybuilder Using Anabolic Steroids

Anabolic steroid use is widespread and has been associated with a variety of pathological conditions. The subject of this case is a 20-year-old amateur bodybuilder who died of sudden cardiopulmonary arrest. He had no previous medical complaints but had a history of anabolic steroid abuse and a hypertrophic heart (515 g) at autopsy. This case presentation will discuss the cardiovascular effects of these drugs and the possible impact of long-term abuse.

The role of cholesterol metabolism and cholesterol transport in carcinogenesis: a review of scientific findings, relevant to future cancer therapeutics.

While the unique metabolic activities of malignant tissues as potential targets for cancer therapeutics has been the subject of several recent reviews, the role of cholesterol metabolism in this context is yet to be fully explored. Cholesterol is an essential component of mammalian cell membranes as well as a precursor of bile acids and steroid hormones. The hypothesis that cancer cells need excess cholesterol and intermediates of the cholesterol biosynthesis pathway to maintain a high level of proliferation is well accepted, however the mechanisms by which malignant cells and tissues reprogram cholesterol synthesis, uptake and efflux are yet to be fully elucidated as potential therapeutic targets. High and low density plasma lipoproteins are the likely major suppliers of cholesterol to cancer cells and tumors, potentially via receptor mediated mechanisms. This review is primarily focused on the role(s) of lipoproteins in carcinogenesis, and their future roles as drug delivery vehicles for targeted cancer chemotherapy.

Evaluation of synthetic/reconstituted high-density lipoproteins as delivery vehicles for paclitaxel

Reconstituted (synthetic) high-density lipoprotein particles carrying paclitaxel (rHDL/PTX) were prepared with substantially higher PTX content than reported earlier. The rHDL/PTX complexes seemed to be primarily spherical nanoparticles when examined via electron microscopy, with a constant composition, molecular weight and exceptional stability even after ultracentrifugation and storage for up to 6 months. The rHDL/PTX nanoparticles had superior cytotoxicity against several cancer cell lines (MCF7, DU145, OV1063 and OVCAR-3), the half maximal inhibitory concentration (IC50) having been found to be 5–20 times lower than that of the free drug. Studies with mice showed that the rHDL/PTX nanoparticles were substantially better tolerated than the corresponding dosages of either Taxol or Abraxane.

Intra-ocular pressure changes during maximal isometric contraction: does this reflect intra-cranial pressure or retinal venous pressure?

Recent publications have suggested that intra-ocular pressure (IOP) may be an indirect assessment of intra-cranial pressure (ICP). Both IOP and ICP have similar physiologic pressure ranges and similar responses to changes in intra-abdominal, intra-thoracic and aortic pressure. Previous studies have demonstrated the relationships between retinal arterial pressure and aortic pressure, intra-ocular pressure and retinal venous pressure, intra-cranial pressure and retinal venous pressure. Power athletes routinely utilize the Valsalva maneuver during weightlifting. In fact there are reports of stroke, cerebral hemorrhage, subarachnoid hemorrhage, conjunctival, foveal and retinal hemorrhage, retinal detachment, hiatal hernia and pneumothorax associated with weightlifting. These events are thought to occur secondary to the extreme pressure elevations that occur in the intra-abdominal, intra-thoracic, intra-cranial, intra-ocular and vascular compartments. To date no human studies have examined the IOP changes that may occur with heavy resistance exercise. Therefore, we recruited power athletes (n = 11), who had participated in prior studies, from the local metropolitan area. The athletes had blood pressure status, drug screening and medical histories performed during previous investigations. Intra-ocular pressure was measured by noncontact tonometry at rest and during maximal isometric contraction. All subjects resting IOP were within normal ranges (mean 13 +/- 2.8 mmHg). Intra-ocular pressures were significantly (p < 0.0001) elevated in each subject during maximal contraction (mean 28 +/- 9.3 mmHg). One subjects IOP reached 46 mmHg during maximal contraction. Linear regression analysis demonstrated a significant linear relationship (r = 0.62, p < 0.0001) in the net change of IOP from rest to maximal contraction for each subject. This study demonstrates that IOP elevates to pathophysiologic levels during resistance exercise. The findings of conjunctival hemorrhages in two subjects further supports IOP being reflective of retinal venous pressure. The enormous pressures generated by power athletes during weightlifting leads to elevations in ICP which obstruct venous outflow leading to hemorrhage and elevations in IOP. The question remains as to whether these intermittent bursts of elevated IOP can lead to long-term pathological sequelae.

Receptor mediated uptake of paclitaxel from a synthetic high density lipoprotein nanocarrier

The purpose of these studies was to determine the mechanism(s) whereby paclitaxel (PTX), is taken up by cancer cells, once encapsulated into synthetic/reconstituted high density lipoprotein (rHDL). The uptake of PTX was found to be facilitated by the scavenger receptor type B-1 (SR-B1) when drug-loaded rHDL particles were incubated with cells that express the SRB1 receptor. Studies with double-labeled, PTX containing rHDL nanoparticles showed that prostate cancer (PC-3) cells incorporated PTX primarily via a selective (SR-B1 type) uptake mechanism. In the presence of a 10-fold excess of plasma HDL, PTX uptake decreased to 30% of the control. These findings suggest that the incorporation of lipophilic drugs by cancer cells from rHDL nanoparticles is facilitated by a receptor mediated (SR-B1) mechanism.

Apolipoprotein D in the aging brain and in Alzheimer's dementia

Abstract Apolipoprotein D (apoD) levels were examined in the temporal cortex as well as an assessment of the location of apoD positive cells within the brain by immunohistochemical and biochemical methods in young control (YC), aged control (AC), and Alzheimer’s demented (AD) probands. Scattered apoD positive astrocytes and oligodendrocytes were found throughout the white matter by immunohistochemistry. ApoD immunoreactivity was also observed In the cerebellar oligodendrocytes of the YC group. There was faint positive apoD staining in scattered cortical astrocytes and a few neurons in the same group. In contrast, some of the AC and all of the AD probands had intense and frequent apoD immunostained cortical astrocytes and pyramidal neurons. The cortical senile plaques and neurofibrillary tangles were apoD immunonegative. No quantitative differences were found between the cortical apoD levels in the AC and AD groups, determined by immunoblotting. ApoD detected in the brain tissue was different in molecular weight (29 kDal) from that seen in CSF or in the serum (32 kDal). Our results indicate apoD is present in the human brain, especially in glial cells, and has increased abundance in the elderly and AD subjects [Neurol Res 2000; 22: 330-336]

Anabolic steroid-induced hepatotoxicity: is it overstated?

OBJECTIVE There have been numerous reports of hepatic dysfunction secondary to anabolic steroid use based on elevated levels of serum aminotransferases. This study was conducted to distinguish between serum aminotransaminase elevations secondary to intense resistance training and anabolic steroid-induced hepatotoxicity in elite bodybuilders. DESIGN This was a case-control study of serum chemistry profiles from bodybuilders using and not using anabolic steroids with comparisons to a cohort of medical students and patients with hepatitis. PARTICIPANTS The participants were bodybuilders taking self-directed regimens of anabolic steroids (n = 15) and bodybuilders not taking steroids (n = 10). Blood chemistry profiles from patients with viral hepatitis (n = 49) and exercising and nonexercising medical students (592) were used as controls. MAIN OUTCOME MEASURES The focus in blood chemistry profiles was aspartate aminotransferase (AST), alanine aminotransferase (ALT), gamma-glutamyltranspeptidase (GGT), and creatine kinase (CK) levels. RESULTS In both groups of bodybuilders, CK, AST, and ALT were elevated, whereas GGT remained in the normal range. In contrast, patients with hepatitis had elevations of all three enzymes: ALT, AST, and GGT. Creatine kinase (CK) was elevated in all exercising groups. Patients with hepatitis were the only group in which a correlation was found between aminotransferases and GGT. CONCLUSION Prior reports of anabolic steroid-induced hepatotoxicity based on elevated aminotransferase levels may have been overstated, because no exercising subjects, including steroid users, demonstrated hepatic dysfunction based on GGT levels. Such reports may have misled the medical community to emphasize steroid-induced hepatotoxicity when interpreting elevated aminotransferase levels and disregard muscle damage. For these reasons, when evaluating hepatic function in cases of anabolic steroid therapy or abuse, CK and GGT levels should be considered in addition to ALT and AST levels as essential elements of the assessment.

Studies on the Apolipoproteins and Lipoproteins of Cord Serum

Summary: Studies on the cord serum lipid transport system were initiated to determine whether there is a correlation between decreased cord serum lipid levels and the absence or diminished level of some or all of the human serum apolipoproteins. Immunologic studies indicated the presence of all the well-characterized apolipoproteins and provided evidence that these apolipoproteins occurred primarily as distinct lipoprotein species with a paucity of association complexes or what others have termed “triglyceride-rich” lipoproteins. Quantitation of the apolipoprotens present in cord serum by electroimmunoassay yielded the following mean levels: A-I = 730 mg/liter; A-II = 410 mg/liter; apolipoprotein B = 280 mg/liter, C-I = 59 mg/liter; C-II = 32 mg/liter; C-III = 65 mg/liter; apolipoprotein D = 37 mg/liter; and apolipoprotein E = 85 mg/liter. Levels of C-I, C-II, and apolipoprotein E approached adult levels (83 to 86% of the adult levels), whereas apolipoproteins B and D were most reduced when compared to the adult concentrations, 29 and 37%, respectively. The three other apolipoproteins were present at approximately one-half the levels found in adults.Speculation: The immunochemical studies on the apolipoprotein levels and lipoprotein forms of cord serum provide part of the data necessary for studying the progressive changes in the human lipid transport system from its fetal form to that of the adult.