David Marais

Non-DNA binding, dominant-negative, human PPARγ mutations cause lipodystrophic insulin resistance

Summary PPARγ is essential for adipogenesis and metabolic homeostasis. We describe mutations in the DNA and ligand binding domains of human PPARγ in lipodystrophic, severe insulin resistance. These receptor mutants lack DNA binding and transcriptional activity but can translocate to the nucleus, interact with PPARγ coactivators and inhibit coexpressed wild-type receptor. Expression of PPARγ target genes is markedly attenuated in mutation-containing versus receptor haploinsufficent primary cells, indicating that such dominant-negative inhibition operates in vivo. Our observations suggest that these mutants restrict wild-type PPARγ action via a non-DNA binding, transcriptional interference mechanism, which may involve sequestration of functionally limiting coactivators.

Chronic melatonin consumption prevents obesity‐related metabolic abnormalities and protects the heart against myocardial ischemia and reperfusion injury in a prediabetic model of diet‐induced obesity

Abstract:  Obesity, a major risk factor for ischemic heart disease, is associated with increased oxidative stress and reduced antioxidant status. Melatonin, a potent free radical scavenger and antioxidant, has powerful cardioprotective effects in lean animals but its efficacy in obesity is unknown. We investigated the effects of chronic melatonin administration on the development of the metabolic syndrome as well as ischemia–reperfusion injury in a rat model of diet‐induced obesity (DIO). Male Wistar rats received a control diet, a control diet with melatonin, a high‐calorie diet, or a high‐calorie diet with melatonin (DM). Melatonin (4 mg/kg/day) was administered in the drinking water. After 16 wk, biometric and blood metabolic parameters were measured. Hearts were perfused ex vivo for the evaluation of myocardial function, infarct size (IFS) and biochemical changes [activation of PKB/Akt, ERK, p38 MAPK, AMPK, and glucose transporter (GLUT)‐4 expression). The high‐calorie diet caused increases in body weight (BW), visceral adiposity, serum insulin and triglycerides (TRIG), with no change in glucose levels. Melatonin treatment reduced the BW gain, visceral adiposity, blood TRIG, serum insulin, homeostatic model assessment index and thiobarbituric acid reactive substances in the DIO group. Melatonin reduced IFS in DIO and control groups and increased percentage recovery of functional performance of DIO hearts. During reperfusion, hearts from melatonin‐treated rats had increased activation of PKB/Akt, ERK42/44 and reduced p38 MAPK activation. Chronic melatonin treatment prevented the metabolic abnormalities induced by DIO and protected the heart against ischemia–reperfusion injury. These beneficial effects were associated with activation of the reperfusion injury salvage kinases pathway.

Reversible Lipid Accumulation and Associated Division Arrest of Mycobacterium avium in Lipoprotein-Induced Foamy Macrophages May Resemble Key Events during Latency and Reactivation of Tuberculosis

ABSTRACT During the dormant phase of tuberculosis, Mycobacterium tuberculosis persists in lung granulomas by residing in foamy macrophages (FM) that contain abundant lipid bodies (LB) in their cytoplasm, allowing bacilli to accumulate lipids as intracytoplasmic lipid inclusions (ILI). An experimental model of FM is presented where bone marrow-derived mouse macrophages are infected with M. avium and exposed to very-low-density lipoprotein (VLDL) as a lipid source. Quantitative analysis of detailed electron microscope observations showed the following results. (i) Macrophages became foamy, and mycobacteria formed ILI, for which host triacylglycerides, rather than cholesterol, was essential. (ii) Lipid transfer occurred via mycobacterium-induced fusion between LB and phagosomes. (iii) Mycobacteria showed a thinned cell wall and became elongated but did not divide. (iv) Upon removal of VLDL, LB and ILI declined within hours, and simultaneous resumption of mycobacterial division restored the number of mycobacteria to the same level as that found in untreated control macrophages. This showed that the presence of ILI resulted in a reversible block of division without causing a change in the mycobacterial replication rate. Fluctuation between ILI either partially or fully extending throughout the mycobacterial cytoplasm was suggestive of bacterial cell cycle events. We propose that VLDL-driven FM constitute a well-defined cellular system in which to study changed metabolic states of intracellular mycobacteria that may relate to persistence and reactivation of tuberculosis.

Recent Origin and Spread of a Common Lithuanian Mutation, G197del LDLR, Causing Familial Hypercholesterolemia: Positive Selection Is Not Always Necessary to Account for Disease Incidence among Ashkenazi Jews

G197del is the most prevalent LDL receptor (LDLR) mutation causing familial hypercholesterolemia (FH) in Ashkenazi Jew (AJ) individuals. The purpose of this study was to determine the origin, age, and population distribution of G197del, as well as to explore environmental and genetic effects on disease expression. Index cases from Israel (n=46), South Africa (n=24), Russia (n=7), The Netherlands (n=1), and the United States (n=1) were enlisted. All trace their ancestry to Lithuania. A highly conserved haplotype (D19S221:104-D19S865:208-D19S413:74) was identified in G197del chromosomes, suggesting the occurrence of a common founder. When two methods were used for analysis of linkage disequilibrium (LD) between flanking polymorphic markers and the disease locus and for the study of the decay of LD over time, the estimated age of the deletion was found to be 20 +/- 7 generations (the 95% confidence interval is 15-26 generations), so that the most recent common ancestor of the mutation-bearing chromosomes would date to the 14th century. This corresponds with the founding of the Jewish community of Lithuania (1338 a.d.), as well as with the great demographic expansion of AJ individuals in eastern Europe, which followed this settlement. The penetrance of mutation-linked severe hypercholesterolemia is high (94% of heterozygotes have a baseline concentration of LDL cholesterol (LDL-C) that is >160 mg/dl), and no significant differences in the mean baseline lipid level of G197del carriers from different countries were found. Polymorphisms of apolipoprotein E and of scavenger-receptor class B type I were observed to have minor effects on the plasma lipid profile. With respect to determinative genetic influences on the biochemical phenotype, there is no evidence that could support the possibility of a selective evolutionary metabolic advantage. Therefore, the founder effect in a rapidly expanding population from a limited number of families remains a simple, parsimonious hypothesis explaining the spread of G197del-LDLR-linked FH in AJ individuals.

A novel Glu421Lys substitution in the lipoprotein lipase gene in pregnancy-induced hypertriglyceridemic pancreatitis

Severe hypertriglyceridemia is an uncommon pathological finding in pregnant women if there is no prior history of hyperlipidemia. A partial reduction in lipoprotein lipase (LPL) activity due to a mutation in the LPL gene, is often an associating factor. Here we report a novel LPL gene mutation (Glu421Lys), in a previously healthy primigravid woman who died from hypertriglyceridemia-induced pancreatitis during the last trimester of pregnancy. The patient was heterozygous for this mutation which a charge inversion in the C-terminal domain of LPL resulting in a moderate reduction in catalytic activity, both in vivo and in vitro. These data support the role of partial LPL deficiency in the pathogenesis of severe gestational hypertriglyceridemia.

Proprotein convertase subtilisin/kexin type 9 inhibition.

Purpose of review There are now ample data that demonstrate that inhibition of PCSK9 (proprotein convertase subtilisin/kexin type 9) can safely lower LDL cholesterol synergistically with statins. Considering that PCSK9 was first identified less than a decade ago, the last few years have shown rapid and remarkable advancements in our understanding and knowledge of the structure and function of PCSK9. Recent findings Therapeutic developments have not lagged far behind with some monoclonal antibodies currently entering phase III trials. Of the many approaches to PCSK9 inhibition, these compounds are the furthest advanced in their clinical development while small molecule oral inhibitors seem a distant prospect. Summary This review summarizes the discovery and history of PCSK9 and in particular its mode of action as an inhibitor of the LDL receptor. It also recapitulates key studies that have demonstrated the potential of inhibiting PCSK9 to further decrease LDL-cholesterol levels safely and synergistically with statins. Finally, we review the strategies that are currently in development to inhibit PCSK9, with a special emphasis on the spectacular results from recent phase-I and phase-II clinical trials.

Community genetics. Its definition 2010

This paper presents a definition of the medical field of community genetics. It starts with a brief historical overview, defines the requirements for an adequate definition, presents the definition, and discusses the constituent parts of the definition.

Lowering the alcohol content of red wine does not alter its cardioprotective properties

BACKGROUND Many epidemiological, clinical and laboratory studies suggest that chronic and moderate consumption of red wine benefits cardiovascular health, because of the alcoholic content or the polyphenols/flavonoids. AIMS The antioxidant and cardioprotective properties of a French red wine (cabernet sauvignon, 12% alcohol by volume) were compared with those of the same wine subjected to reverse osmosis for partial removal of alcohol (6% alcohol by volume). METHODS Antioxidant capacity was assessed in vitro using the oxygen radical absorbance capacity (ORAC) assay. To test the cardioprotective effect of 12% v. 6% wine, the drinking water of rats used for controls was supplemented with red wine (12% or 6%). After 10 days, hearts were isolated on a Langendorff system and subjected to 30 minutes of global ischaemia plus 30 minutes of reperfusion (I/R). RESULTS No differences in antioxidant capacity were observed between wine of 12% and 6% alcohol content (n=8 per group). Control hearts subjected to I/R presented a rate pressure product (heart rate x left ventricular developed pressure, expressed as a percentage of baseline value) of 16±4% (mean±standard error). Pretreatment with wine 12% or 6% improved the rate pressure product to 40±6% and 43±6%, respectively (p<0.05 v. control). CONCLUSION Our findings suggest that the reduction of alcohol content from 12% to 6% in wine did not alter its antioxidant and cardioprotective properties. Moderate and regular consumption of lower alcohol content wines may confer beneficial effects without the risks associated with traditional wines of higher alcohol content.

Dysbetalipoproteinemia: an extreme disorder of remnant metabolism.

Purpose of review Lipoprotein metabolism and the role of apolipoprotein E in the pathogenesis of dysbetalipoproteinemia. Recent findings Remnant lipoproteins, modulated by lifestyle and genetic factors, are atherogenic. Dysbetalipoproteinemia could be viewed as a monogenic disorder of remnant metabolism. Summary Elevated plasma triglyceride and cholesterol concentrations (mixed hyperlipidemias) are commonly encountered and dysbetaliproteinemia should be considered in this setting. Dysbetalipoproteinemia (remnant clearance disease, Fredrickson type III hyperlipidemia) is an uncommon dyslipoproteinemia related to mutations in apolipoprotein E that disrupt the clearance of remnants of triglyceride-rich lipoproteins; it may be overlooked because xanthomata of the skin and/or tendons occur in a minority of patients. The diagnosis ideally requires the demonstration of remnant lipoprotein accumulation and a genetic cause. Genotyping for apolipoprotein E2 may not prove the diagnosis as it may be associated with low plasma lipid values. The recent association of remnant lipoproteins with atherosclerosis along with many factors that modulate remnant lipoprotein metabolism underscores the importance of recognising dysbetalipoproteinemia as an extreme state of remnant lipoprotein accumulation. Although there may be some differences between remnants in the general population and dysbetalipoproteinemia, it is clear that remnants promote atherosclerosis. Current treatment strategies are adequate but new strategies could also be of benefit in dysbetalipoproteinemia.

Cardiology–cardiothoracic subspeciality training in South Africa : a position paper of the South Africa Heart Association

Abstract Over the past decades, South Africa has undergone rapid demographic changes, which have led to marked increases in specific cardiac disease categories, such as rheumatic heart disease (now predominantly presenting in young adults with advanced and symptomatic disease) and coronary artery disease (with rapidly increasing prevalence in middle age). The lack of screening facilities, delayed diagnosis and inadequate care at primary, secondary and tertiary levels have led to a large burden of patients with heart failure. This leads to suffering of the patients and substantial costs to society and the healthcare system. In this position paper, the South African Heart Association (SA Heart) National Council members have summarised the current state of cardiology, cardiothoracic surgery and paediatric cardiology reigning in South Africa. Our report demonstrates that there has been minimal change in the number of successfully qualified specialists over the last decade and, therefore, a de facto decline per capita. We summarise the major gaps in training and possible interventions to transform the healthcare system, dealing with the colliding epidemic of communicable disease and the rapidly expanding epidemic of non-communicable disease, including cardiac disease.