DPP4 inhibition mitigates ANG II-mediated kidney immune activation and injury in male mice

Recent evidence suggests that dipeptidyl peptidase-4 (DPP4) inhibition with saxagliptin (Saxa) is renoprotective under comorbid conditions associated with activation of the renin-angiotensin-aldosterone system (RAAS), such as diabetes, obesity, and hypertension, which confer a high cardiovascular risk. Immune system activation is now recognized as a contributor to RAAS-mediated tissue injury, and, importantly, immunomodulatory effects of DPP4 have been reported. Accordingly, we examined the hypothesis that DPP4 inhibition with Saxa attenuates angiotensin II (ANG II)-induced kidney injury and albuminuria via attenuation of immune activation in the kidney. To this end, male mice were infused with either vehicle or ANG II (1,000 ng/kg/min, s.c.) for 3 wk and received either placebo or Saxa (10 mg/kg/day, p.o.) during the final 2 wk. ANG II infusion increased kidney, but not plasma, DPP4 activity in vivo as well as DPP4 activity in cultured proximal tubule cells. The latter was prevented by angiotensin receptor blockade with olmesartan. Further, ANG II induced hypertension and kidney injury characterized by mesangial expansion, mitochondrial damage, reduced brush border megalin expression, and albuminuria. Saxa inhibited DPP4 activity ∼50% in vivo and attenuated ANG II-mediated kidney injury, independent of blood pressure. Further mechanistic experiments revealed mitigation by Saxa of proinflammatory and profibrotic mediators activated by ANG II in the kidney, including CD8⁺ T cells, resident macrophages (CD11b^hiF4/80^loLy6C^-), and neutrophils. In addition, Saxa improved ANG II suppressed anti-inflammatory regulatory T cell and T helper 2 lymphocyte activity. Taken together, these results demonstrate, for the first time, blood pressure-independent involvement of renal DPP4 activation contributing to RAAS-dependent kidney injury and immune activation.NEW & NOTEWORTHY This work highlights the role of dipeptidyl peptidase-4 (DPP4) in promoting ANG II-mediated kidney inflammation and injury. Specifically, ANG II infusion in mice led to increases in blood pressure and kidney DPP4 activity, which then led to activation of CD8⁺ T cells, Ly6C^- macrophages, and neutrophils and suppression of anti-inflammatory T helper 2 lymphocytes and regulatory T cells. Collectively, this led to kidney injury, characterized by mesangial expansion, mitochondrial damage, and albuminuria, which were mitigated by DPP4 inhibition independent of blood pressure reduction.

The global spectrum of protein-coding pharmacogenomic diversity

Differences in response to medications have a strong genetic component. By leveraging publically available data, the spectrum of such genomic variation can be investigated extensively. Pharmacogenomic variation was extracted from the 1000 Genomes Project Phase 3 data (2504 individuals, 26 global populations). A total of 12 084 genetic variants were found in 120 pharmacogenes, with the majority (90.0%) classified as rare variants (global minor allele frequency <0.5%), with 52.9% being singletons. Common variation clustered individuals into continental super-populations and 23 pharmacogenes contained highly differentiated variants (FST>0.5) for one or more super-population comparison. A median of three clinical variants (PharmGKB level 1A/B) was found per individual, and 55.4% of individuals carried loss-of-function variants, varying by super-population (East Asian 60.9%>African 60.1%>South Asian 60.3%>European 49.3%>Admixed 39.2%). Genome sequencing can therefore identify clinical pharmacogenomic variation, and future studies need to consider rare variation to understand the spectrum of genetic diversity contributing to drug response.

Mycophenolate mofetil and animal models

Mycophenolate mofetil (MMF), is the morpholinoethyl ester of mycophenolic acid (MPA). Though initially developed as an anti-rejection treatment, MMF is beginning to find application in more common immune-mediated diseases. MMF has been shown to be effective against transplant-associated vascular disease, lupus and other inflammatory diseases via multiple mechanisms in several animal models. MMF treatment blocks the proliferation of T cells and B cells, attenuates the production of autoreactive IgG and IgM, diminishes complement deposition, and reduces the production of multiple proinflammatory cytokines including TNF-α, IFN-γ, IL-2, IL-3, IL-4, IL-5, IL-6 and IL-12. It also increases production of the anti-inflammatory mediator IL-10. In addition, MMF reduces the infiltration of immune cells into sites of inflammation by interfering with the expression of cell-surface molecules critical for this process, including MHC class II, CD40, CD80, CD86, I-A, and ICAM-1. Additional mechanisms involving mannosylation and N-linked glycosylation of cell-surface molecules are only beginning to be investigated. This article will focus on the contribution of animal models of disease as investigational tools in the development of MMF as an immunomodulatory drug. The use of mice, rats, rabbits, monkeys, baboons and interspecific xenografts will be discussed.

Mycophenolate mofetil as an immunomodulatory silver bullet in atherogenesis?

Atherosclerotic vascular disease is a chronic disorder of the vasculature with a substantial impact on society. Although the availability of statins has represented an unparalleled improvement in the treatment of patients with such cardiovascular disease, even more effective measures are required to reverse this disorder with a continuously growing incidence. The classification of atherosclerosis as an inflammatory disorder has prompted the hypothesis that immunomodulation could comprise a novel anti-atherosclerotic strategy. Mycophenolate mofetil (MMF) has various anti-atherogenic effects on major components of the atherosclerotic plaque such as T-lymphocytes, monocytes/macrophages and the endothelium. MMF can inhibit leukocyte recruitment to the subendothelium and the subsequent reduced activation of leukocytes will translate into attenuation of subendothelial crosstalk between T-cells and macrophages. This cascade of events will interrupt the self-perpetuating pro-inflammatory environment within the arterial wall, the hallmark of atherosclerotic vascular disease.

Enhanced immune response to MMP3 stimulation in microglia expressing mutant huntingtin

Huntington's Disease (HD) is an inherited neurodegenerative disease caused by a polyglutamine expansion in the huntingtin protein. The YAC128 mouse model of HD expresses the full-length human huntingtin protein with 128 CAG repeats and replicates the phenotype and neurodegeneration that occur in HD. Several studies have implicated a role for neuroinflammation in HD pathogenesis. Studies on presymptomatic HD patients have illustrated microgliosis (activated microglia) in brain regions affected in HD. Mutant huntingtin expressing isolated primary monocytes (human HD patients) and primary macrophages (YAC128) are overactive in response to lipopolysaccharide (LPS) stimulation. In this study we demonstrate that cultured primary microglia (the resident immune cells of the brain cells) from YAC128 mice differentially express a wide number of cytokines compared to wildtype microglia cultures in response to LPS. Furthermore, this study outlines a direct interaction between mutant huntingtin and cytokine secretion in HD microglia. Increased cytokine release in YAC128 microglia can be blocked by cannabinoid activation or by mutant huntingtin knockdown with anti-sense oligonucleotide treatment. Matrix metalloprotease 3 (MMP3), an endogenous neuronal activator of microglia, also induces increased cytokine release from YAC128 microglia compared to wildtype microglia. We found elevated MMP levels in HD CSF, and MMP levels correlate with disease severity in HD. These data support a novel role for MMPs and microglial activation in HD pathogenesis. With an improved understanding of the specific cellular processes involved in HD neuroinflammation, novel therapeutic agents targeting these processes can be developed and hold great promise in the treatment of HD.

A novel microdeletion affecting the CETP gene raises HDL-associated cholesterol levels

We describe a novel, inherited 16q13 microdeletion that removes cholesteryl ester transfer protein (CETP) and several nearby genes. The proband was originally referred for severe childhood-onset obesity and moderate developmental delay, but his fasting lipid profile revealed relatively high levels of high density lipoprotein cholesterol (HDL-C) and relatively low levels of low density lipoprotein cholesterol (LDL-C) for age, despite his obesity. Testing of first-degree relatives identified two other microdeletion carriers. Functional assays in affected individuals showed decreased CETP mRNA expression and enzymatic activity. This microdeletion may or may not be pathogenic for obesity and developmental delay, but based on the lipid profile, the functional studies, and the phenotype of other patients with loss-of-function mutations of CETP, we believe this microdeletion to be antipathogenic for cardiovascular disease.

Use of genetic technologies to compare medicines

In order to ensure that patients receive the safest and most effective medicines possible, it is often necessary to compare medicines and assess the extent to which they are similar in their clinical impact. Full clinical trials with appropriate endpoints remain the only method to compare the clinical impact of two medicines with absolute certainty. Other available methods (including physicochemical analysis, genomics, and transcriptomics) can provide partial information about certain aspects of a medicine's biological impact, with possible clinical implications. Especially for biologics and non-biological complex drugs, which are more difficult to characterize by physicochemical means than small molecules, genomics and transciptomic studies can yield valuable insights for physicians, regulators, and drug developers. In this review, we cite and summarize a variety of studies that exemplify the emerging science of applying genomics and transcriptomics technologies to compare medicines. We discuss key aspects of experimental design, conduct of genetic assays, and advanced data analysis, all of which are critical for the successful execution of such studies. Finally, we propose new areas for which such studies can be applied to maximize patient benefit and reduce safety issues.

The emerging era of pharmacogenomics: current successes, future potential, and challenges

The vast range of genetic diversity contributes to a wonderful array of human traits and characteristics. Unfortunately, a consequence of this genetic diversity is large variability in drug response between people, meaning that no single medication is safe and effective in everyone. The debilitating and sometimes deadly consequences of adverse drug reactions (ADRs) are a major and unmet problem of modern medicine. Pharmacogenomics can uncover associations between genetic variation and drug safety and has the potential to predict ADRs in individual patients. Here we review pharmacogenomic successes leading to changes in clinical practice, as well as clinical areas probably to be impacted by pharmacogenomics in the near future. We also discuss some of the challenges, and potential solutions, that remain for the implementation of pharmacogenomic testing into clinical practice for the significant improvement of drug safety.

Replication of TPMT and ABCC3 genetic variants highly associated with cisplatin-induced hearing loss in children

Cisplatin is a widely used chemotherapeutic agent for the treatment of solid tumors. A serious complication of cisplatin treatment is permanent hearing loss. The aim of this study was to replicate previous genetic findings in an independent cohort of 155 pediatric patients. Associations were replicated for genetic variants in TPMT (rs12201199, P = 0.0013, odds ratio (OR) 6.1) and ABCC3 (rs1051640, P = 0.036, OR 1.8). A predictive model combining variants in TPMT, ABCC3, and COMT with clinical variables (patient age, vincristine treatment, germ-cell tumor, and cranial irradiation) significantly improved the prediction of hearing-loss development as compared with using clinical risk factors alone (area under the curve (AUC) 0.786 vs. 0.708, P = 0.00048). The novel combination of genetic and clinical factors predicted the risk of hearing loss with a sensitivity of 50.3% and a specificity of 92.7%. These findings provide evidence to support the importance of TPMT, COMT, and ABCC3 in the prediction of cisplatin-induced hearing loss in children.

Validation of variants in SLC28A3 and UGT1A6 as genetic markers predictive of anthracycline-induced cardiotoxicity in children

BACKGROUND

The use of anthracyclines as effective antineoplastic drugs is limited by the occurrence of cardiotoxicity. Multiple genetic variants predictive of anthracycline-induced cardiotoxicity (ACT) in children were recently identified. The current study was aimed to assess replication of these findings in an independent cohort of children.

PROCEDURE

. Twenty-three variants were tested for association with ACT in an independent cohort of 218 patients. Predictive models including genetic and clinical risk factors were constructed in the original cohort and assessed in the current replication cohort.

RESULTS

. We confirmed the association of rs17863783 in UGT1A6 and ACT in the replication cohort (P = 0.0062, odds ratio (OR) 7.98). Additional evidence for association of rs7853758 (P = 0.058, OR 0.46) and rs885004 (P = 0.058, OR 0.42) in SLC28A3 was found (combined P = 1.6 × 10(-5) and P = 3.0 × 10(-5), respectively). A previously constructed prediction model did not significantly improve risk prediction in the replication cohort over clinical factors alone. However, an improved prediction model constructed using replicated genetic variants as well as clinical factors discriminated significantly better between cases and controls than clinical factors alone in both original (AUC 0.77 vs. 0.68, P = 0.0031) and replication cohort (AUC 0.77 vs. 0.69, P = 0.060).

CONCLUSIONS

. We validated genetic variants in two genes predictive of ACT in an independent cohort. A prediction model combining replicated genetic variants as well as clinical risk factors might be able to identify high- and low-risk patients who could benefit from alternative treatment options.

Two novel mutations in apolipoprotein C3 underlie atheroprotective lipid profiles in families

Apolipoprotein C3 (APOC3) mutations carriers typically display high plasma high-density lipoprotein cholesterol (HDL-C) and low triglycerides (TGs). We set out to investigate the prevalence and clinical consequences of APOC3 mutations in individuals with hyperalphalipoproteinemia. Two novel mutations (c.-13-2A>G and c.55+1G>A) and one known mutation (c.127G>A;p.Ala43Thr) were found. Lipid profiles and apoCIII isoform distributions were measured. c.55+1G>A mutation carriers displayed higher HDL-C percentiles (35.6 ± 35.8 vs 99.0 ± 0, p = 0.002) and lower TGs (0.51 (0.37-0.61) vs 1.42 (1.12-1.81) mmol/l, p = 0.007) and apoCIII levels (4.24 ± 1.57 vs 7.33 ± 3.61 mg/dl, p = 0.18). c.-13-2A>G mutation carriers did not display significantly different HDL-C levels (84.0 ± 30.0 vs 63.7 ± 45.7, p = 0.50), a trend towards lower TGs [0.71 (0.54 to 0.78) vs 0.85 (0.85 to -) mmol/l, p = 0.06] and significantly lower apoCIII levels (3.09 ± 1.08 vs 11.45 ± 1.06 mg/dl, p = 0.003). p.Ala43Thr mutation carriers displayed a trend towards higher HDL-C percentiles (91.2 ± 31.8 vs 41.0 ± 29.7 mmol/l, p = 0.06) and significantly lower TGs [0.58 (0.36-0.63) vs 0.95 (0.71-1.20) mmol/l, p = 0.02] and apoCIII levels (4.92 ± 2.33 vs 6.60 ± 1.60, p = 0.25). Heterozygosity for APOC3 mutations results in high HDL-C and low TGs and apoCIII levels. This favourable lipid profile in patients with genetically low apoCIII levels holds promise for current studies investigating the potential of apoCIII inhibition as a novel therapeutic in cardiovascular disease prevention.

Providing predictive testing for Huntington disease via telehealth: results of a pilot study in British Columbia, Canada

Predictive testing (PT) for Huntington disease (HD) usually requires several in-person appointments which acts as a barrier to testing for those from remote regions. This pilot study reports the use of telehealth PT to examine whether such telehealth testing improves access to HD PT while maintaining quality of care and support. Individuals underwent PT via the telehealth protocol or standard in-person protocol and were asked to complete surveys regarding their experience. Results reveal no significant differences between the in-person-tested and telehealth-tested groups with respect to quality of care, information, counselling and support. The majority of participants in both groups stated that pre-test counselling had provided them with sufficient knowledge about the advantages and disadvantages of undergoing testing, the opportunity to ask questions, and the ability to make an informed decision. The majority of participants in both groups were satisfied by the manner in which results were delivered and stated they had received sufficient information regarding the implications of these results. This study reveals that telehealth PT improves access while maintaining quality of care and support.

"Grasping the grey": patient understanding and interpretation of an intermediate allele predictive test result for Huntington disease

Since the discovery of the genetic mutation underlying Huntington disease (HD) and the development of predictive testing, the genetics of HD has generally been described as straightforward; an individual receives either mutation-positive or negative predictive test results. However, in actuality, the genetics of HD is complex and a small proportion of individuals receive an unusual predictive test result called an intermediate allele (IA). Unlike mutation-positive or negative results, IAs confer uncertain clinical implications. While individuals with an IA will usually not develop HD, there remains an unknown risk for their children and future generations to develop the disorder. The purpose of this study was to explore how individuals understood and interpreted their IA result. Interviews were conducted with 29 individuals who received an IA result and 8 medical genetics service providers. Interviews were analyzed using the constant comparative method and the coding procedures of grounded theory. Many participants had difficulty "Grasping the Grey" (i.e. understanding and interpreting their IA results) and their family experience, beliefs, expectations, and genetic counseling influenced the degree of this struggle. The theoretical model developed informs clinical practice regarding IAs, ensuring that this unique subset of patients received appropriate education, support, and counseling.

Human Mendelian pain disorders: a key to discovery and validation of novel analgesics

We have utilized a novel application of human genetics, illuminating the important role that rare genetic disorders can play in the development of novel drugs that may be of relevance for the treatment of both rare and common diseases. By studying a very rare Mendelian disorder of absent pain perception, congenital indifference to pain, we have defined Nav1.7 (endocded by SCN9A) as a critical and novel target for analgesic development. Strong human validation has emerged with SCN9A gain-of-function mutations causing inherited erythromelalgia (IEM) and paroxysmal extreme pain disorder, both Mendelian disorder of spontaneous or easily evoked pain. Furthermore, variations in the Nav1.7 channel also modulate pain perception in healthy subjects as well as in painful conditions such as osteoarthritis and Parkinson disease. On the basis of this, we have developed a novel compound (XEN402) that exhibits potent, voltage-dependent block of Nav1.7. In a small pilot study, we showed that XEN402 blocks Nav1.7 mediated pain associated with IEM thereby demonstrating the use of rare genetic disorders with mutant target channels as a novel approach to rapid proof-of-concept. Our approach underscores the critical role that human genetics can play by illuminating novel and critical pathways pertinent for drug discovery.

Early treatment with olmesartan prevents juxtamedullary glomerular podocyte injury and the onset of microalbuminuria in type 2 diabetic rats

BACKGROUND

Studies were performed to determine if early treatment with an angiotensin II (Ang II) receptor blocker (ARB), olmesartan, prevents the onset of microalbuminuria by attenuating glomerular podocyte injury in Otsuka Long-Evans Tokushima Fatty (OLETF) rats with type 2 diabetes mellitus.

METHODS

OLETF rats were treated with either a vehicle, olmesartan (10 mg/kg/day) or a combination of nonspecific vasodilators (hydralazine 15 mg/kg/day, hydrochlorothiazide 6 mg/kg/day, and reserpine 0.3 mg/kg/day; HHR) from the age of 7-25 weeks.

RESULTS

OLETF rats were hypertensive and had microalbuminuria from 9 weeks of age. At 15 weeks, OLETF rats had higher Ang II levels in the kidney, larger glomerular desmin-staining areas (an index of podocyte injury), and lower gene expression of nephrin in juxtamedullary glomeruli, than nondiabetic Long-Evans Tokushima Otsuka (LETO) rats. At 25 weeks, OLETF rats showed overt albuminuria, and higher levels of Ang II in the kidney and larger glomerular desmin-staining areas in superficial and juxtamedullary glomeruli compared to LETO rats. Reductions in mRNA levels of nephrin were also observed in superficial and juxtamedullary glomeruli. Although olmesartan did not affect glucose metabolism, it decreased blood pressure and prevented the renal changes in OLETF rats. HHR treatment also reduced blood pressure, but did not affect the renal parameters.

CONCLUSIONS

This study demonstrated that podocyte injury occurs in juxtamedullary glomeruli prior to superficial glomeruli in type 2 diabetic rats with microalbuminuria. Early treatment with an ARB may prevent the onset of albuminuria through its protective effects on juxtamedullary glomerular podocytes.

CAG repeat expansion in Huntington disease determines age at onset in a fully dominant fashion

OBJECTIVE

Age at onset of diagnostic motor manifestations in Huntington disease (HD) is strongly correlated with an expanded CAG trinucleotide repeat. The length of the normal CAG repeat allele has been reported also to influence age at onset, in interaction with the expanded allele. Due to profound implications for disease mechanism and modification, we tested whether the normal allele, interaction between the expanded and normal alleles, or presence of a second expanded allele affects age at onset of HD motor signs.

METHODS

We modeled natural log-transformed age at onset as a function of CAG repeat lengths of expanded and normal alleles and their interaction by linear regression.

RESULTS

An apparently significant effect of interaction on age at motor onset among 4,068 subjects was dependent on a single outlier data point. A rigorous statistical analysis with a well-behaved dataset that conformed to the fundamental assumptions of linear regression (e.g., constant variance and normally distributed error) revealed significance only for the expanded CAG repeat, with no effect of the normal CAG repeat. Ten subjects with 2 expanded alleles showed an age at motor onset consistent with the length of the larger expanded allele.

CONCLUSIONS

Normal allele CAG length, interaction between expanded and normal alleles, and presence of a second expanded allele do not influence age at onset of motor manifestations, indicating that the rate of HD pathogenesis leading to motor diagnosis is determined by a completely dominant action of the longest expanded allele and as yet unidentified genetic or environmental factors.

Phosphate Metabolism in Cardiorenal Metabolic Disease

Hyperphosphatemia is a major risk factor for cardiovascular disease, abnormalities of mineral metabolism and bone disease, and the progression of renal insufficiency in patients with chronic renal disease. In early renal disease, serum phosphate levels are maintained within the 'normal laboratory range' by compensatory increases in phosphaturic hormones such as fibroblast growth factor-23 (FGF-23). An important co-factor for FGF-23 is Klotho; a deficiency in Klotho plays an important role in the pathogenesis of hyperphosphatemia, renal tubulointerstitial disease, and parathyroid and bone abnormalities. Clinical hyperphosphatemia occurs when these phosphaturic mechanisms cannot counterbalance nephron loss. Hyperphosphatemia is associated with calcific uremic arteriolopathy and uremic cardiomyopathy, which may explain, in part, the epidemiologic connections between phosphate excess and cardiovascular disease. However, no clinical trials have been conducted to establish a causal relationship, and large, randomized trials with hard endpoints are urgently needed to prove or disprove the benefits and risks of therapy. In summary, hyperphosphatemia accelerates renal tubulointerstitial disease, renal osteodystrophy, as well as cardiovascular disease, and it is an important mortality risk factor in patients with chronic kidney disease.

Novel mutations in scavenger receptor BI associated with high HDL cholesterol in humans

The scavenger receptor class B, member 1 (SR-BI), is a key cellular receptor for high-density lipoprotein (HDL) in mice, but its relevance to human physiology has not been well established. Recently a family was reported with a mutation in the gene encoding SR-BI and high HDL cholesterol (HDL-C). Here we report two additional individuals with extremely high HDL-C (greater than the 90th percentile for age and gender) with rare mutations in the gene encoding SR-BI. These mutations segregate with high HDL-C in family members of each proband and are associated with a 37% increase in plasma HDL-C in heterozygous individuals carrying them. Both mutations occur at highly conserved positions in the large extracellular loop region of SR-BI and are predicted to impair the function of the SR-BI protein. Our findings, combined with the prior report of a single mutation in the gene encoding SR-BI, further validate that mutations in SR-BI are a rare but recurring cause of elevated HDL-C in humans.

Adoption and the communication of genetic risk: experiences in Huntington disease

Adoption agencies can use genetic information to determine the eligibility of prospective adoptive parents and to establish a child's suitability for adoption. We describe experiences and implications of communicating genetic risk for Huntington disease (HD) in the context of adoption. A secondary analysis was employed using data collected from a cross-sectional survey (n = 233) and two qualitative studies on the psychosocial effects of predictive testing for HD. We demonstrate several ethical and practical challenges in the search for and communication of genetic information for adoptees and their birth relatives. We also found that concern for adoption discrimination was reported by 13.7% of survey respondents (n = 32). Concerns were higher among tested respondents than those who had not been tested (n = 29 vs n = 3, p = 0.010). However, more respondents were concerned about being discriminated based on their family history (FHx) vs their genetic test results (GTR) (concern based on FHx: n = 18 vs based on GTR: n = 1 vs based on both: n =10). These findings contribute to the limited empirical literature by offering evidence on the experiences and implications of communicating genetic risk information in the context of adoption with reference to HD.

Magnetic resonance spectroscopy biomarkers in premanifest and early Huntington disease

OBJECTIVES

To evaluate in vivo brain metabolite differences in control subjects, individuals with premanifest Huntington disease (pre-HD), and individuals with early HD using ¹H magnetic resonance spectroscopy (MRS) and to assess their relationship with motor performance.

METHODS

Eighty-five participants (30 controls, 25 pre-HD, and 30 early HD) were recruited as part of the TRACK-HD study. Eighty-four were scanned at 3 T with single-voxel spectroscopy in the left putamen. Disease burden score was >220 among pre-HD individuals. Subjects underwent TRACK-HD motor assessment including Unified Huntington's Disease Rating Scale (UHDRS) motor scoring and a novel quantitative motor battery. Statistical analyses included linear regression and one-way analysis of variance.

RESULTS

Total N-acetylaspartate (tNAA), a neuronal integrity marker, was lower in early HD (∼15%) vs controls (p < 0.001). N-acetylaspartate (NAA), a constituent of tNAA, was lower in pre-HD (∼8%) and early HD (∼17%) vs controls (p < 0.05). The glial cell marker, myo-inositol (mI), was 50% higher in early HD vs pre-HD (p < 0.01). In early HD, mI correlated with UHDRS motor score (R² = 0.23, p < 0.05). Across pre-HD and early HD, tNAA correlated with performance on a tongue pressure task (R² = 0.30, p < 0.0001) and with disease burden score (R² = 0.17, p < 0.005).

CONCLUSIONS

We demonstrate lower putaminal tNAA in early HD compared to controls in a cross-section of subjects. A novel biomarker role for mI in early HD was also identified. These findings resolve disagreement in the literature about the role of MRS as an HD biomarker. We conclude that putaminal MRS measurements of NAA and mI are promising potential biomarkers of HD onset and progression.

Cholesterol efflux via ATP-binding cassette transporter A1 (ABCA1) and cholesterol uptake via the LDL receptor influences cholesterol-induced impairment of beta cell function in mice

AIMS/HYPOTHESIS

Cellular cholesterol accumulation is an emerging mechanism for beta cell dysfunction in type 2 diabetes. Absence of the cholesterol transporter ATP-binding cassette transporter A1 (ABCA1) results in increased islet cholesterol and impaired insulin secretion, indicating that impaired cholesterol efflux leads to beta cell dysfunction. In this study, we aimed to determine the role of the LDL receptor (LDLr) in islet cholesterol uptake and to assess the contributions of cholesterol uptake compared with efflux to islet cholesterol levels.

METHODS

Islet cholesterol and beta cell function were assessed in mice lacking LDLr (Ldlr(-/-)), or apolipoprotein E (Apoe(-/-)), as well as in mice with beta-cell-specific deficiency of Abca1 crossed to Ldlr(-/-) mice.

RESULTS

Hypercholesterolaemia resulted in increased islet cholesterol levels and decreased beta cell function in Apoe(-/-) mice but not in Ldlr(-/-) mice, suggesting that the LDL receptor is required for cholesterol uptake leading to cholesterol-induced beta cell dysfunction. Interestingly, when wild-type islets with functional LDL receptors were transplanted into diabetic, hypercholesterolaemic mice, islet graft function was normal compared with Ldlr(-/-) islets, suggesting that compensatory mechanisms can maintain islet cholesterol homeostasis in a hypercholesterolaemic environment. Indeed, transplanted wild-type islets had increased Abca1 expression. However, lack of the Ldlr did not protect Abca1(-/-) mice from islet cholesterol accumulation, suggesting that cholesterol efflux is the critical regulator of cholesterol levels in islets.

CONCLUSIONS/INTERPRETATION

Our data indicate that islet cholesterol levels and beta cell function are strongly influenced by LDLr-mediated uptake of cholesterol into beta cells. Cholesterol efflux mediated by ABCA1, however, can compensate in hypercholesterolaemia to regulate islet cholesterol levels in vivo.

Unstable familial transmissions of Huntington disease alleles with 27-35 CAG repeats (intermediate alleles)

There are inconsistent reports regarding the likelihood of repeat instability for alleles with 27-35 CAG repeats in the Huntington disease (HD) gene. We have examined the intergenerational stability of such intermediate alleles in 51 families from the University of British Columbia's DNA and Tissue Bank for Huntington Disease Research (UBC-HD Databank). A total of 181 transmissions were identified, with 30% (n = 54/181) of the alleles being unstable upon transmission. The unstable transmissions included both expansions (n = 37) and contractions (n = 17) of CAG size. Of the expanded alleles, 68% (n = 25/37) expanded into the HD range (>36 CAG). Therefore, 14% (n = 25/181) of the 27-35 CAG allele transmissions examined expanded into the disease-associated range resulting in a new mutation for HD. Significantly, of these new mutations, 40% (n = 10/25) originated from an allele with 35 CAG repeats with CAG repeat expansions ranging from +1 CAG to +23 CAG. The proportion of new mutations in the UBC-HD Databank is consistent with the most recent new mutation rate for HD, estimated to be at least 10%. The observed difference in the stability of HD intermediate allele transmissions in this data set and in other studies may be a reflection of a small sample size. Alternately, these inconsistencies may indicate an underlying difference in genetic factors which influence repeat instability between the different populations examined. Additional studies determining the frequency and magnitude of repeat instability in this CAG repeat range and factors that influence instability are urgently needed. Until we understand the clinical implications of HD alleles with 27-35 CAG repeats and establish reliable risks of instability, we should exercise caution when translating these results to the clinic.

Enhanced susceptibility to pancreatitis in severe hypertriglyceridaemic lipoprotein lipase-deficient mice and agonist-like function of pancreatic lipase in pancreatic cells

BACKGROUND AND AIMS

Recurrent pancreatitis is a common complication of severe hypertriglyceridaemia in patients with various gene mutations in lipoprotein lipase (LPL) or apolipoprotein CII. However, the exact pathogenetic mechanism has not yet been defined.

METHODS

Susceptibility to pancreatitis in LPL-deficient mice was compared with that of wild-type mice after intraperitoneal injections of caerulein by determination of amylase release and pancreatic pathological scores. The effect of chylomicrons and fatty acids on enzyme release, Ca(2+) signalling and cell injury in isolated pancreatic acinar cells from wild-type and LPL-deficient mice was investigated.

RESULTS

Caerulein induced higher levels of serum amylase and more severe inflammation in the pancreas of LPL-deficient mice than in wild-type mice. Addition of free fatty acids or chylomicrons to isolated pancreatic acinar cells led to the release of amylase and caused cell injury at higher concentrations. The effect of chylomicrons was partially blocked by orlistat, an inhibitor of pancreatic lipase. These results suggest that increased concentrations of free fatty acids from chylomicron hydrolysis by pancreatic lipase can induce acinar cell injury. Surprisingly, pancreatic lipase, whether in its active or inactive state could act like an agonist by inducing amylase secretion without cell injury. It caused an increase in cGMP levels and conversion of cell-damaging sustained elevations of [Ca(2+)] to normal Ca(2+) oscillations.

CONCLUSIONS

LPL-deficient mice with severe hypertriglyceridaemia display enhanced susceptibility to acute pancreatitis. High levels of chylomicrons and free fatty acids result in pancreatic cell injury. Pancreatic lipase has a dual effect: generating free fatty acids from chylomicrons and preventing Ca(2+) overload in pancreatic acinar cells.

Plasma apolipoprotein AV levels in mice are positively associated with plasma triglyceride levels

Apolipoprotein AV (apoAV) overexpression causes a decrease in plasma triglyceride (TG) levels, while deficiency of apoAV causes hypertriglyceridemia in both men and mice. However, contrary to what would be expected, plasma apoAV and TG levels in humans are positively correlated. To address this apparent paradox, we determined plasma apoAV levels in various mouse models with median TG levels ranging from 30 mg/dl in wild-type mice to 2089 mg/dl in glycosylphosphatidylinositol-anchored HDL binding protein 1-deficient mice. The data show that apoAV and TG levels are positively correlated in mice (r = +0.798, P < 0.001). In addition, we show that LPL gene transfer caused a simultaneous decrease in TG and apoAV in LPL-deficient mice. The combined data suggest that apoAV levels follow TG levels due to an intimate link between the apoAV molecule and TG-rich lipoproteins, comprising both secretion and removal of these lipoproteins. Taken together, the data suggest that higher plasma apoAV levels reflect an increased demand for plasma TG hydrolysis under normal physiological conditions.

The role of free fatty acids, pancreatic lipase and Ca+ signalling in injury of isolated acinar cells and pancreatitis model in lipoprotein lipase-deficient mice

AIM AND METHODS

Recurrent pancreatitis is a common complication of severe hypertriglyceridaemia (HTG) often seen in patients carrying various gene mutations in lipoprotein lipase (LPL). This study investigates a possible pathogenic mechanism of cell damage in isolated mouse pancreatic acinar cells and of pancreatitis in LPL-deficient and in wild type mice.

RESULTS

Addition of free fatty acids (FFA) or of chylomicrons to isolated pancreatic acinar cells caused stimulation of amylase release, and at higher concentrations it also caused cell damage. This effect was decreased in the presence of the lipase inhibitor orlistat. Surprisingly, pancreatic lipase whether in its active or inactive state could act like an agonist by inducing amylase secretion, increasing cellular cGMP levels and converting cell damaging sustained elevations of [Ca(2+)](cyt) to normal Ca(2+) oscillations. Caerulein increases the levels of serum amylase and caused more severe inflammation in the pancreas of LPL-deficient mice than in wild type mice.

CONCLUSION

We conclude that high concentrations of FFA as present in the plasma of LPL-deficient mice and in patients with HTG lead to pancreatic cell damage and are high risk factors for the development of acute pancreatitis. In addition to its enzymatic effect which leads to the generation of cell-damaging FFA from triglycerides, pancreatic lipase also prevents Ca(2+) overload in pancreatic acinar cells and, therefore, counteracts cell injury.

Genotypic Approaches to Therapy in Children (GATC): using information technology to improve drug safety

Adverse drug reactions (ADRs) are a major cause of morbidity and mortality in children. Current models of ADR surveillance have repeatedly demonstrated little pragmatic value to practicing clinicians. ADR reporting rates in the US and Canada suggest that only 5% of ADRs are reported. The Genotypic Approaches to Therapy in Children (GATC) network was established to identify and solve drug safety problems in paediatrics. We hypothesized that genetic polymorphisms underlie a significant portion of concentration-dependent ADRs in children. Our objective was to establish an ADR active surveillance network in paediatric hospitals across Canada. Surveillance clinicians evaluate clinical information from ADR cases and drug-matched controls, and collected DNA samples from all patients. The surveillance network will enable the identification of predictive genomic-markers for ADRs. With this knowledge, children at risk can be identified before therapy is initiated and enable personalized adjustments to therapy based on genetic make-up.

Regulation of huntingtin palmitoylation and its role in Huntington Diseases

Huntington’s Disease (HD) is an autosomal dominant neurodegenerative disorder characterized by motor, cognitive, and psychiatric deficits and selective neuronal cell death. The causative mutation in HD is an expansion of the N-terminal polyglutamine tract in huntingtin (htt), which results in altered trafficking of mutant htt and enhanced toxicity to striatal neurons. Post-translational modification by the lipid palmitate has been shown to play a critical role in the trafficking and function of many proteins, including htt. It has been previously demonstrated that huntingtin-interacting protein 14 (HIP14) is a palmitoyl transferase that palmitoylates htt. Previous characterization of HIP14 demonstrated a reduced interaction with mutant htt resulting in reduced palmitoylation, suggesting that palmitoylation may play a role in the pathogenesis of HD. Most recently, we have identified cysteine 214 as a major site of htt palmitoylation in the N-terminus of htt, close to the site of polyglutamine expansion. It was demonstrated that mutation of this site, rendering htt palmitoylation-resistant, results in increased neuronal toxicity, enhanced inclusion formation, and in altered trafficking of htt. Remarkably, mutation of the palmitoylation site in wild type htt also resulted in enhanced toxicity similar to that seen in mutant htt. Together, these previous studies suggest a critical role of palmitoylation in htt trafficking and function. Based on this preliminary work, we are characterizing the enzymatic regulation of huntingtin palmitoylation. Exploring htt palmitoylation in a number of existing and new mouse models imparts key insights into how this process is regulated in vivo. We are also exploring the relationship between palmitoylation and other post-translational modifications of htt. These studies will lead to an understanding of the regulation of palmitoylation of huntingtin in vivo, as well as setting the precedent to understand the general role of palmitoylation in a wide range of other human diseases. Ultimately, this may lead to identification of new therapeutic targets and treatments for patients. F.B.J.Y. is supported by a Canadian Institutes of Health Research Walter and Jessie Boyd & Charles Scriver - Child and Family Research Institute - UBC MD/PhD Studentship Award. She also receives funding from the Michael Smith Foundation for Health Research as a Junior Trainee.

Managing genetic discrimination: strategies used by individuals found to have the Huntington disease mutation

The introduction of predictive testing for Huntington disease (HD) over 20 years ago has led to the advent of a new group of individuals found to have the HD mutation that are currently asymptomatic, yet destined in all likelihood to become affected at some point in the future. Genetic discrimination, a social risk associated with predictive testing, is the differential treatment of individuals based on genotypic difference rather than physical characteristics. While evidence for genetic discrimination exists, little is known about how individuals found to have the HD mutation cope with the potential for or experiences of genetic discrimination. The purpose of this study was to explore how individuals found to have the HD mutation manage the risk and experience of genetic discrimination. Semi-structured individual interviews were conducted with 37 individuals who were found to have the HD mutation and analysed using grounded theory methods. The findings suggest four main strategies: "keeping low", minimizing, pre-empting and confronting genetic discrimination. Strategies varied depending on individuals' level of engagement with genetic discrimination and the nature of the experience (actual experience of genetic discrimination or concern for its potential). This exploratory framework may explain the variation in approaches and reactions to genetic discrimination among individuals living with an increased risk for HD and may offer insight for persons at risk for other late-onset genetic diseases to cope with genetic discrimination.

Loss-of-function mutations in the Nav1.7 gene underlie congenital indifference to pain in multiple human populations

Congenital indifference to pain (CIP) is a rare condition in which patients have severely impaired pain perception, but are otherwise essentially normal. We identified and collected DNA from individuals from nine families of seven different nationalities in which the affected individuals meet the diagnostic criteria for CIP. Using homozygosity mapping and haplotype sharing methods, we narrowed the CIP locus to chromosome 2q24-q31, a region known to contain a cluster of voltage-gated sodium channel genes. From these prioritized candidate sodium channels, we identified 10 mutations in the SCN9A gene encoding the sodium channel protein Nav1.7. The mutations completely co-segregated with the disease phenotype, and nine of these SCN9A mutations resulted in truncation and loss-of-function of the Nav1.7 channel. These genetic data further support the evidence that Nav1.7 plays an essential role in mediating pain in humans, and that SCN9A mutations identified in multiple different populations underlie CIP.

Predictive testing for Huntington disease: interpretation and significance of intermediate alleles

Direct mutation analysis for Huntington disease (HD) became possible in 1993 with the identification of an expanded CAG trinucleotide repeat as the mutation underlying the disease. Expansion of CAG length beyond 35 repeats may be associated with the clinical presentation of HD. HD has never been seen in a person with a CAG size of <36 repeats. Intermediate alleles are defined as being below the affected CAG range but have the potential to expand to >35 CAG repeats within one generation. Thus, children of intermediate allele carriers have a low risk of developing HD. Currently, the intermediate allele range for HD is between 27 and 35 CAG repeats. In this study, we review the current knowledge on intermediate alleles for HD including the CAG repeat range, the intermediate allele frequency, and the clinical implications of an intermediate allele predictive test result. The factors influencing CAG repeat expansion, including the CAG size of the intermediate allele, the sex and age of the transmitting parent, the family history, and the HD gene sequence and haplotype, will also be reviewed.

Als2-deficient mice exhibit disturbances in endosome trafficking associated with motor behavioral abnormalities

ALS2 is an autosomal recessive form of spastic paraparesis (motor neuron disease) with juvenile onset and slow progression caused by loss of function of alsin, an activator of Rac1 and Rab5 small GTPases. To establish an animal model of ALS2 and derive insights into the pathogenesis of this illness, we have generated alsin-null mice. Cytosol from brains of Als2(-/-) mice shows marked diminution of Rab5-dependent endosome fusion activity. Furthermore, primary neurons from Als2(-/-) mice show a disturbance in endosomal transport of insulin-like growth factor 1 (IGF1) and BDNF receptors, whereas neuronal viability and endocytosis of transferrin and dextran seem unaltered. There is a significant decrease in the size of cortical motor neurons, and Als2(-/-) mice are mildly hypoactive. Altered trophic receptor trafficking in neurons of Als2(-/-) mice may underlie the histopathological and behavioral changes observed and the pathogenesis of ALS2.

Ethyl-EPA in Huntington disease: A double-blind, randomized, placebo-controlled trial

BACKGROUND

Preliminary evidence suggests beneficial effects of pure ethyl-eicosapentaenoate (ethyl-EPA) in Huntington disease (HD).

METHODS

A total of 135 patients with HD were randomized to enter a multicenter, double-blind, placebo-controlled trial on the efficacy of 2 g/d ethyl-EPA vs placebo. The Unified Huntington's Disease Rating Scale (UHDRS) was used for assessment. The primary end point was outcome at 12 months on the Total Motor Score 4 subscale (TMS-4). Analysis of covariance (ANCOVA) and a chi2 test on response, defined as absence of increase in the TMS-4, were performed.

RESULTS

A total of 121 patients completed 12 months, and 83 did so without protocol violations (PP cohort). Intent-to-treat (ITT) analysis revealed no significant difference between ethyl-EPA and placebo for TMS-4. In the PP cohort, ethyl-EPA proved better than placebo on the chi2 test on TMS-4 (p < 0.05), but missed significance on ANCOVA (p = 0.06). Secondary end points (ITT cohort) showed no benefit of ethyl-EPA but a significantly worse outcome in the behavioral severity and frequency compared with placebo. Exploring moderators of the efficacy of ethyl-EPA on TMS-4 showed a significant interaction between treatment and a factor defining patients with high vs low CAG repeats. Reported adverse events were distributed equally between treatment arms.

CONCLUSIONS

Ethyl-eicosapentaenoate (ethyl-EPA) (purity > 95%) had no benefit in the intent-to-treat cohort of patients with Huntington disease, but exploratory analysis revealed that a significantly higher number of patients in the per protocol cohort, treated with ethyl-EPA, showed stable or improved motor function. Further studies of the potential efficacy of ethyl-EPA are warranted.

A homozygous HAMP mutation in a multiply consanguineous family with pseudo-dominant juvenile hemochromatosis

Juvenile hemochromatosis (JH) is an autosomal recessive condition that leads to significant morbidity due to early onset systemic iron overload. The majority of families with JH link to chromosome 1q and were recently found to have mutations in the HFE2 gene encoding hemojuvelin; however, several JH families have been reported to have mutations in the HAMP gene encoding hepcidin. Here, we report a multiply consanguineous family with a father and daughter showing iron overload consistent with JH. Sequence analysis of HAMP revealed homozygosity for amino acid substitution C78T due to a c.233G > A mutation. This mutation disrupts one of eight highly conserved cysteines that are believed to be critical for the function of the active enzyme. This finding adds support to the importance of the role of these conserved cysteines in the activity of hepcidin.

Proteomic analysis of homocysteine inhibition of microvascular endothelial cell angiogenesis

Although homocysteine (Hcy) inhibits angiogenesis in vivo and in vitro, the mechanism(s) underlying this phenomenon are largely unclear. The hypothesis of the present work is that Hcy, while inducing the expression of antiangiogenic factors, inhibits the production of angiogenic factors. Mouse brain microvascular endothelial cells (MVEC) were cultured in the presence and absence of 20 microM Hcy for 24 hr in serum-free medium. Cell homogenates were incubated with Trans-Signal Angiogenesis Antibody Array containing antibodies to angiogenic activators (ANG, HGF, leptin, VEGF, IL-6, IL-8, PIGF, FGF-alpha/beta, TNF-alpha and TGF-alpha) and inhibitors (IFN-gamma, IL-12, IP-10, TIMP-1 and -2). The array membranes were scanned and normalized with positive controls. Angiogenesis and formation of capillaries were measured by culturing the MVEC in Matrigels. The capillary-like structures were identified by transmission microscopy. Hcy decreased the expression of leptin, IL-6, -8, PIGF, FGF-alpha and VEGF, while the levels of anti-angiogenic IL-12, IP-10 (chemokine) and TIMP-1 were increased by Hcy. The vascular tube-like structures by MVEC were decreased by increased Hcy. However, the addition of VEGF to Hcy-treated MVEC ameliorated the decreased Hcy-mediated capillary formation. The results suggest that Hcy inhibits angiogenesis, in part, by decreasing VEGF and increasing TIMP-1.

Specific caspase interactions and amplification are involved in selective neuronal vulnerability in Huntington's disease

Huntington's disease (HD) is an autosomal dominant progressive neurodegenerative disorder resulting in selective neuronal loss and dysfunction in the striatum and cortex. The molecular pathways leading to the selectivity of neuronal cell death in HD are poorly understood. Proteolytic processing of full-length mutant huntingtin (Htt) and subsequent events may play an important role in the selective neuronal cell death found in this disease. Despite the identification of Htt as a substrate for caspases, it is not known which caspase(s) cleaves Htt in vivo or whether regional expression of caspases contribute to selective neuronal cells loss. Here, we evaluate whether specific caspases are involved in cell death induced by mutant Htt and if this correlates with our recent finding that Htt is cleaved in vivo at the caspase consensus site 552. We find that caspase-2 cleaves Htt selectively at amino acid 552. Further, Htt recruits caspase-2 into an apoptosome-like complex. Binding of caspase-2 to Htt is polyglutamine repeat-length dependent, and therefore may serve as a critical initiation step in HD cell death. This hypothesis is supported by the requirement of caspase-2 for the death of mouse primary striatal cells derived from HD transgenic mice expressing full-length Htt (YAC72). Expression of catalytically inactive (dominant-negative) forms of caspase-2, caspase-7, and to some extent caspase-6, reduced the cell death of YAC72 primary striatal cells, while the catalytically inactive forms of caspase-3, -8, and -9 did not. Histological analysis of post-mortem human brain tissue and YAC72 mice revealed activation of caspases and enhanced caspase-2 immunoreactivity in medium spiny neurons of the striatum and the cortical projection neurons when compared to controls. Further, upregulation of caspase-2 correlates directly with decreased levels of brain-derived neurotrophic factor in the cortex and striatum of 3-month YAC72 transgenic mice and therefore suggests that these changes are early events in HD pathogenesis. These data support the involvement of caspase-2 in the selective neuronal cell death associated with HD in the striatum and cortex.

Heterozygosity for ABCA1 gene mutations: effects on enzymes, apolipoproteins and lipoprotein particle size

A cohort of 13 female and 14 male heterozygotes for ATP binding cassette A1 (ABCA1) gene defects was directly compared with 13 and 14 unaffected female and male family members of almost exact same age. The activities of three proteins that play key roles in HDL metabolism were measured in addition to extensive lipid and (apo) lipoprotein subfraction analysis. Compared to controls, LCAT activity was reduced by 15% in affected subjects (P < 0.001) while PLTP activity was unaffected. Interestingly, CETP activity was elevated by 50% in the heterozygote siblings of one kindred but was unaffected in heterozygotes of the three other families. With respect to lipids, the heterozygotes had normal total cholesterol (TC), and LDL-cholesterol concentrations but presented with a trend towards increased triglyceride levels (13%; P = 0.08). HDL metabolism, by contrast, was severely affected as illustrated by 40% reductions in HDL-cholesterol (P < 0.001) with concomitant reductions in apoAI (25%; P < 0.001) levels and in lipoprotein subfraction LpAI (28%; P < 0.001), LpAI:AII (24%; P=0.014), and LpCIII:nonB (34%; P < 0.001) concentrations. We furthermore observed reduced average HDL particle size (5%; P = 0.004; 16% in female and 3.6% in male) and reduced plasma apoCIII concentration (15%; P = 0.006) while apoAII, apoAIV, apoE and apoB levels were unchanged. In conclusion, heterozygosity for ABCA1 defects was associated with reduced LCAT activity in absence of effects on PLTP activity. Of special interest was our finding that the effects of compromised ABCA1 function on HDL were more pronounced in women than in men.

A new model for prediction of the age of onset and penetrance for Huntington's disease based on CAG length

Huntington's disease (HD) is a neurodegenerative disorder caused by an unstable CAG repeat. For patients at risk, participating in predictive testing and learning of having CAG expansion, a major unanswered question shifts from "Will I get HD?" to "When will it manifest?" Using the largest cohort of HD patients analyzed to date (2913 individuals from 40 centers worldwide), we developed a parametric survival model based on CAG repeat length to predict the probability of neurological disease onset (based on motor neurological symptoms rather than psychiatric onset) at different ages for individual patients. We provide estimated probabilities of onset associated with CAG repeats between 36 and 56 for individuals of any age with narrow confidence intervals. For example, our model predicts a 91% chance that a 40-year-old individual with 42 repeats will have onset by the age of 65, with a 95% confidence interval from 90 to 93%. This model also defines the variability in HD onset that is not attributable to CAG length and provides information concerning CAG-related penetrance rates.