Timothy C. Hardman

New lipid-lowering drugs: an update

Lipid lowering is established as a proven intervention to reduce atherosclerosis and its complications. Statins form the basis of care but are not able to treat all aspects of dyslipidaemia. Many novel therapeutic compounds are being developed. These include additional therapeutics for low‐density lipoprotein cholesterol, for example, thyroid mimetics (thyroid receptor beta‐agonists), antisense oligonucleotides or microsomal transfer protein inhibitors (MTPI); triglycerides, for example, novel peroxosimal proliferator activating receptors agonists, MTPIs, diacylglycerol acyl transferase‐1 inhibitors and high‐density lipoprotein cholesterol (HDL‐C), for example, mimetic peptides; HDL delipidation strategies and cholesterol ester transfer protein inhibitors and modulators of inflammation, for example, phospholipase inhibitors. Gene therapy for specific rare disorders, for example, lipoprotein lipase deficiency using alipogene tiparvovec is also in clinical trials. Lipid‐lowering drugs are likely to prove a fast‐developing area for novel treatments as possible synergies exist between new and established compounds for the treatment of atherosclerosis.

Development and potential role of type-2 sodium-glucose transporter inhibitors for management of type 2 diabetes.

There is a recognized need for new treatment options for type 2 diabetes mellitus (T2DM). Recovery of glucose from the glomerular filtrate represents an important mechanism in maintaining glucose homeostasis and represents a novel target for the management of T2DM. Recovery of glucose from the glomerular filtrate is executed principally by the type 2 sodium-glucose cotransporter (SGLT2). Inhibition of SGLT2 promotes glucose excretion and normalizes glycemia in animal models. First reports of specifically designed SGLT2 inhibitors began to appear in the second half of the 1990s. Several candidate SGLT2 inhibitors are currently under development, with four in the later stages of clinical testing. The safety profile of SGLT2 inhibitors is expected to be good, as their target is a highly specific membrane transporter expressed almost exclusively within the renal tubules. One safety concern is that of glycosuria, which could predispose patients to increased urinary tract infections. So far the reported safety profile of SGLT2 inhibitors in clinical studies appears to confirm that the class is well tolerated. Where SGLT2 inhibitors will fit in the current cascade of treatments for T2DM has yet to be established. The expected favorable safety profile and insulin-independent mechanism of action appear to support their use in combination with other antidiabetic drugs. Promotion of glucose excretion introduces the opportunity to clear calories (80–90 g [300–400 calories] of glucose per day) in patients that are generally overweight, and is expected to work synergistically with weight reduction programs. Experience will most likely lead to better understanding of which patients are likely to respond best to SGLT2 inhibitors, and under what circumstances.

HIV lipodystrophy and its metabolic consequences: implications for clinical practice.

ABSTRACT Background: The introduction of highly active antiretroviral therapy (HAART) around 1996 markedly reduced mortality and morbidity from human immunodeficiency virus (HIV) infection. As life expectancy has improved, the chronic complications of HIV and HAART have become increasingly relevant. Scope: This article provides an overview of the HIV-associated lipodystrophy, its pathogenesis and its clinical consequences (based on a search strategy in PubMed including literature published to November 2007). Findings: Lipodystrophy syndrome is characterized by abnormal fat distribution syndrome associated with metabolic disturbances and includes insulin resistance, deranged glucose and lipid metabolism. It is associated with increased risks of progression to type 2 diabetes and cardiovascular disease. Robust diagnostic criteria are required for lipodystrophy, and subsequent prospective cohort studies and randomized controlled trials are then required to determine the etiology and prognosis of lipodystrophy, and to evaluate therapeutic interventions for this consequence of HAART. Therapies to improve insulin resistance have been tried but they are frequently ineffective, and are limited by potential toxicity in this population. Hence, current management options for HIV associated lipodystrophy are limited and are mostly based on avoidance of risk factors and switching of antiretroviral drugs. Conclusion: As the ‘3 by 5 strategy’ of providing HIV drugs to the developing world is implemented worldwide, the numbers of patients adhering to antiretroviral medicines is dramatically increasing. One must be aware that in reducing the burden of acute retroviral disease, the treatments proposed might lead to significant rates of metabolic complications and further exacerbation of the epidemic of diabetes and cardiovascular disease.

Inhibition of pre-protein convertase serine kexin-9 (PCSK-9) as a treatment for hyperlipidaemia

Introduction: Pre-protein convertase subtilisin kexin (PCSK)-9 is a newly discovered protein involved in intracellular and extracellular regulation of low-density lipoprotein receptor (LDLR) expression. Autosomal dominant activating mutations in PCSK-9 cause familial hypercholesterolaemia whereas inactivating mutations in man reduce LDL cholesterol (LDL-C) and are associated with a decreased lifetime risk of cardiovascular events. Areas covered: As PCSK-9 binds to the LDLR, a number of approaches involving small molecule or peptide inhibition of binding, antibody-mediated inactivation of binding and the use of antisense oligonucleotides are being investigated as therapeutic approaches to lower LDL-C in man. This article reviews the biochemistry and physiology of PCSK-9 and details the efforts made to design novel molecules with the ability to inhibit PCSK-9 activity. Work in animal models has confirmed that reducing PCSK-9 expression can reduce atherosclerosis in mice, rats and primates. Monoclonal antibodies such as REGN-727 and AMG-145 have been shown to reduce LDL-C in patients with familial hypercholesterolaemia already treated with statins or healthy normocholesterolaemic controls. Expert opinion: PCSK-9 inhibition is a potentially interesting novel addition to the armamentarium of LDL-C reducing drugs. Its effects in reducing LDL-C will need to be confirmed to reduce CVD events in large-scale clinical trials.

Controversies surrounding erythrocyte sodium-lithium countertransport

Background Interest originally arose in ouabain-insensitive lithium transport across erythrocyte membranes when it was found that lithium could substitue for sodium, either undergoing 1 :1 lithium exchange or 1 :1 sodium-lithium countertransport in a manner that follows Michaelis- Menten kinetics. Elevation of the sodium-lithium countertransport activity in hypertension was first noted in 1980 and found to be a genetically linked phenomenon. This observation has since been confirmed on several occasions and associations with other dieases such as diabetes have been noted. Nevertheless, many unanswered questions remain about the clinical significance of disturbed sodium-lithium countertransport and its pathological basis. Methods Traditional methods for characterizing the sodium-lithium countertransporter have depended on determining differences between lithium fluxes into sodium-rich and sodium-free media. There have been inherent problems in deciding on suitable sodium substitutes. Of the available alternatives, choline has emerged as having advantages over magnesium. Reports in the literature have often failed to take into account varied assay conditions, making comparisons of data from different laboratories difficult A further complexity has been the realization that sodium-lithium countertransport activity incorporates two key elements in the form of Vmax and km. Kinetic studies have shown independent variation in these two parameters with various disease states. Results Much of the published work to date has continued to rely on measurement of countertransport activity, with magnesium acting as the predominant sodium-substitute. This has occurred despite the undoubted benefits obtained from kinetic analysis. Where kinetics of the sodium-lithium countertransporter have been determined, there have emerged clear associations between Vmax and environmental influences such as plasma lipids with elevated values in dyslipidaemic states including diabetes. The affinity constant, km, is more clearly under genetic control and has independent associations with vascular disease. Conclusions Study of the erythrocyte sodium-lithium countertransporter has revealed interesting relationships between altered behaviour of the transporter and specific disease states. Although still somewhat of an enigma, this transporter is emerging as an important membrane constituent whose further study may help us to understand the molecular mechanisms leading to vascular disease.

Erythrocyte sodium-lithium countertransport and blood pressure in identical twin pairs discordant for insulin dependent diabetes.

OBJECTIVE--To investigate whether insulin dependent diabetes is responsible for the abnormal behaviour of the carrier in sodium-lithium countertransport and whether the diabetic state is associated with rise in blood pressure. DESIGN--Case-control study. SETTING--London teaching hospital. SUBJECTS--44 twin pairs discordant for insulin dependent diabetes living in United Kingdom and 44 healthy control subjects matched for age, sex, and body mass index. None of the twin pairs or the controls had evidence of microalbuminuria. MAIN OUTCOME MEASURES--Sodium-lithium countertransport activity in erythrocytes and arterial blood pressure. RESULTS--The mean (95% confidence interval) sodium-lithium countertransport activity (mmol Li per litre of red blood cells per h) of the diabetic twins (0.291 (0.244 to 0.338)) was similar to that of their non-diabetic cotwins (0.247 (0.204 to 0.290)); both values were significantly higher than that of the controls (0.187 (0.157 to 0.216); p < 0.05). In addition, systolic blood pressure was higher in those twins with diabetes (127 (122 to 133) mm Hg) than in the non-diabetic cotwins (122 (117 to 127) mm Hg; p < 0.01). There were no significant differences in mean diastolic blood pressure between any of the groups studied. CONCLUSIONS--The raised erythrocyte sodium-lithium countertransport activity in the diabetic twins compared with the controls seems to be inherited rather than a consequence of overt diabetes. The higher systolic blood pressure in diabetic twins than non-diabetic cotwins indicates that insulin dependent diabetes does exert a small influence on systolic blood pressure.

New therapies to reduce low-density lipoprotein cholesterol.

Purpose of review Lipid-lowering is an intervention that reduces atherosclerosis and its complications. Statins currently form the standard of care but are not able to reduce low-density lipoprotein cholesterol (LDL-C) adequately in all patients – particularly those with familial hypercholesterolaemia and those with statin intolerance. Recent findings Combination therapy with statins is well established and ezetimibe is often used as an additional LDL-C-lowering agent reducing LDL-C by 20%. However, its clinical efficacy still remains controversial. Newer, more potent methods of LDL-C reduction are in development. Both lomitapide, a microsomal transfer protein inhibitor (MTPI), and mipomersen, an antisense oligonucleotide (ASO), have been shown to improve LDL-C levels by 25–50% in patients with homozygous familial hypercholesterolaemia. In patients with heterozygous familial hypercholesterolaemia or statin intolerance antibody-based inhibitors of preprotein convertase subtilisin/kexin 9 (PCSK9) produce reductions in LDL-C of 30–65%. Cholesterol ester transfer protein inhibitors (CETPIs) reduce LDL-C by 30–40% as well as raising levels of high-density lipoprotein cholesterol (HDL-C) and may also have a role as additional LDL-C-reducing drugs. Summary Surrogate outcome trials will be required with lomitapide or mipomersen to confirm their effects in homozygous familial hypercholesterolaemia and clinical endpoint trials will be needed for PCSK9 and CETPIs if these are to be used widely.

Sarcoidosis: the links between epidemiology and aetiology

Sarcoidosis is a multisystem inflammatory disease, the aetiology of which has still to be resolved. The proposed mechanism is that a susceptible genotype is exposed to one or more potential antigens. A sustained inflammatory response follows, which ultimately results in pathognomonic granuloma formation. Various clinical phenotypes exist with specific genetic associations influencing disease susceptibility, protection, and clinical progression. Occupational and environmental factors, including microbial elements, may then effect the development of this disease. Sarcoidosis is a heterogeneous disease, showing geographic and racial variation in clinical presentation. It demonstrates a familial tendency and clear genotype associations. Additionally, it appears to cluster within closely associated populations (eg, work colleagues) and appears to be related to selected occupations and environmental exposures. Frequently occult, but occasionally fatal, this disease has a very variable prognosis. It is also unusual in having no specific biomarker. The epidemiology and multiple factors that appear to influence the aetiology of sarcoidosis illustrate why this disease state is frequently described as a clinical enigma.

The apolipoprotein E2 allele modulates activity and maximal velocity of the sodium–lithium countertransporter

BACKGROUND Alterations in erythrocyte sodium-lithium countertransport (SLC) activity and its maximal velocity (Vmax) are associated with hypertension and hypertriglyceridemia. The presence of apolipoprotein (apo) E variants is associated with hypertriglyceridemia. This study investigated the relationship between apoE phenotype and SLC kinetics. METHODS Cardiovascular risk factors and SLC kinetics were measured in 171 subjects and 69 controls. Apolipoprotein E phenotypes were determined by Western blotting. RESULTS Patients were 51% male, aged 56+/-13 years, with a blood pressure (BP) of 134+/-22/81+/-11 mm Hg, total cholesterol of 6.71+/-1.57 (256+/-61 mg/dL); median triglycerides 1.65 mmol/L (146 mg/dL) (range, 0.31 to 9.85 mmol/L; 27 to 872 mg/dL) and high-density lipoprotein (HDL) 1.39+/-0.43 mmol/L (54+/-16.6 mg/dL); fasting glucose 4.91+/-0.61 mmol/L (88.5+/-11.0 mg/dL); median insulin 11.7 IU/L (range, 3.7 to 39.8 IU/L). Phenotype frequencies were E3/E3 56%, E2/E3 14%, E2/E2 1%, E3/E4 27%, and E4/E4 2%. The SLC activity, Vmax, and sodium affinity (Km) were not significantly different with respect to apoE phenotype in simple analysis by Kruskal Wallis test. However, in multiple regression analysis after exclusion of BP, a strong co-correlate of SLC activity, the presence of an apoE2 allele was associated reduced activity (beta = -0.061; P = .01) along with HDL:apoA1 ratio (beta = -0.170; P < .001), whereas for the kinetic parameter Vmax, associations were found with triglyceride (beta = 0.029; P = .04), HDL:apoA1 ratio (beta = -0.186; P = .03) and the presence of an apoE2 allele (beta = -0.089; P = .04). CONCLUSIONS These findings suggest that the apoE phenotype may modulate SLC activity and that the presence of an apoE2 allele phenotype is associated with lower SLC activity and Vmax.

Relation between sodium–lithium countertransport and hypertriglyceridemia in type V hyperlipidemia

Sodium-lithium countertransport (SLC) kinetics were measured in 30 patients with type V hyperlipidemia, 30 patients with type IIB hyperlipidemia on similar treatment, and 30 age- and sex-matched healthy controls. Clinical and laboratory data including basic anthropometry and blood pressure were obtained and blood was taken for detailed lipid biochemistry, glucose, insulin, and leptin measurements. Patients with type V hyperlipidemia were normotensive but more obese than controls, had elevated triglycerides, very low-density lipoprotein, glucose, and insulin; and reduced HDL cholesterol compared with type IIb controls. The median SLC activity (0.23 v 0.21 mmol Li+/L RBC/h) and median maximal velocity (0.33 v 0.31 mmol Li+/L RBC/h) were increased, but not significantly, compared to controls. In patients with type V hyperlipidemia SLC maximal velocity correlated with log triglycerides (r2 = 0.853; P < .001) and log very low-density lipoprotein (VLDL) triglycerides (r2 = 0.947; P < .001). Sodium-lithium countertransport maximal velocity correlated weakly with the homeostasis model assessment index of insulin resistance (r2 = 0.224; P = .06). The sodium affinity of the transporter did not differ between the groups and was independent of any of clinical or biochemical parameter studied. We conclude that VLDL triglyceride is strongly correlated with SLC maximal velocity and activity in patients with type V hyperlipidemia.