Dyslipidemia-Induced Neuropathy in Mice: The Role of oxLDL/LOX-1

OBJECTIVE

Neuropathy is a frequent and severe complication of diabetes. Multiple metabolic defects in type 2 diabetic patients result in oxidative injury of dorsal root ganglia (DRG) neurons. Our previous work focused on hyperglycemia clearly demonstrates induction of mitochondrial oxidative stress and acute injury in DRG neurons; however, this mechanism is not the only factor that produces neuropathy in vivo. Dyslipidemia also correlates with the development of neuropathy, even in pre-diabetic patients. This study was designed to explore the contribution of dyslipidemia in neuropathy.

RESEARCH DESIGN AND METHODS

Mice (n = 10) were fed a control (10% kcal %fat) or high-fat (45% kcal %fat) diet to explore the impact of plasma lipids on the development of neuropathy. We also examined oxidized lipid–mediated injury in cultured DRG neurons from adult rat using oxidized LDLs (oxLDLs).

RESULTS

Mice on a high-fat diet have increased oxLDLs and systemic and nerve oxidative stress. They develop nerve conduction velocity (NCV) and sensory deficits prior to impaired glucose tolerance. In vitro, oxLDLs lead to severe DRG neuron oxidative stress via interaction with the receptor lectin-like oxLDL receptor (LOX)-1 and subsequent NAD(P)H oxidase activity. Oxidative stress resulting from oxLDLs and high glucose is additive.

CONCLUSIONS

Multiple metabolic defects in type 2 diabetes directly injure DRG neurons through different mechanisms that all result in oxidative stress. Dyslipidemia leads to high levels of oxLDLs that may injure DRG neurons via LOX-1 and contribute to the development of diabetic neuropathy.Our work is focused on understanding the mechanisms that lead to diabetic neuropathy and developing rational therapeutic interventions. Hyperglycemia clearly leads to peripheral nerve injury through the development of systemic and neuronal oxidative stress (1–6). An emerging idea is that dyslipidemia also contributes to the development of diabetic neuropathy (7,8). Lipid profiles are commonly abnormal early in the course of type 2 diabetes in a temporal pattern that correlates with the presence of diabetic neuropathy, and we recently reported that elevated triglyceride levels predict a more rapid disease course (9,10). In addition, several large-scale trials of type 2 diabetic patients point to early dyslipidemia as a major independent risk factor for the development of diabetic neuropathy (11).In experimental diabetes, the complex etiology of diabetic neuropathy is difficult to explore due to the multiple sources of nerve injury, including hyperglycemia, advanced glycation end products, systemic oxidative stress, and altered growth factor availability (12). Furthermore, lipid profiles of mice differ from human patients in that the majority of plasma cholesterol is transported in HDL and LDL levels are constitutively low (13). Mice with genetically increased plasma cholesterol have accelerated atherosclerosis that renders them unsuitable for neuropathy studies (13). Several studies (14–16) explored the role of a high-fat diet in the development of both diabetes and diabetic complications. Susceptibility to neuropathy is mouse strain dependent; the constitution of the diet is another important factor. One study (17) suggests that a high-fat diet produces neuropathy independent of hyperglycemia, and the present study explores a potential mechanism of high-fat–induced neuropathy.Because high-fat diets increase plasma LDLs and pre-diabetes is associated with systemic oxidative stress (18), we proposed that oxidized LDLs (oxLDLs) will be elevated in mice fed a high-fat diet. Furthermore, we predicted that increased oxLDLs may produce dorsal root ganglia (DRG) neuron injury through binding the lectin-like oxLDL receptor (LOX)-1 in a similar manner to vascular endothelial cells (19) and renal tubular cells (20). The activation of LOX-1 on endothelial cells leads to intracellular oxidative stress and inflammation and a feed-forward cycle of injury in diabetes, since both oxLDLs and glucose increase LOX-1 expression (21,22).In this study, we used high-fat feeding in the C57/BL6 mouse strain using a 45-kcal %fat (mostly from lard) diet. We demonstrate morphological and functional evidence of neuropathy prior to loss of glucose regulation in agreement with clinical findings (10,23,24). This is associated with significant increases in plasma oxLDLs. We assessed oxLDL-mediated injury in cultured DRG neurons from adult rats. oxLDLs directly lead to oxidative stress and injury in DRG neurons via LOX-1. DRG neuron injury is partially induced via activation of NAD(P)H oxidase. We conclude that diet-induced plasma oxLDLs can produce neuron injury and may be a contributing factor in the development of neuropathy in pre-diabetes or diabetes.     

Surgical device closure a new technique of ASD closure

Background Conventional approach of atrial septal defect (ASD) closure with cardio pulmonary bypass using mid sternotomy, minimally invasive or endoscopic technique is time tested. We decided to use custom made device with direct minimally invasive approach without cardio pulmonary bypass. Percutaneous transfemoral route using custom made device is a well established procedure performed by interventional cardiologist with occasional trauma and vessels. Method We performed the procedure in 3 patients of secundum ASD deemed adequate for device closure. We used a mini Right anterior thoracotomy approach using a double umbrella device which was implanted through direct Right Atrial puncture. Results In two patients we were successful in deploying the device. The proedure lasted 30 minutes with small infra Mammary scar and the post operative period was uneventful. In the third case where our attempt at surgical device closure failed the inferior margin was only one mm. The optimal size device kept slipping into the right atrium when the guide-wire was tugged after final deployment. The placement of an oversize device distorted the mitral valve, may causing regurgitation. Conclusion We think that this is a simple and safe technique of secundum ASD closure without cardio pulmonary bypass.     

Age-related effect on the concentration of collagen crosslinks in human osteonal and interstitial bone tissue

Collagen crosslinks are important to the quality of bone and may be contributors to the age-related increase in bone fracture. This study was performed to investigate whether age and gender effects on collagen crosslinks are similar in osteonal and interstitial bone tissues. Forty human cadaveric femurs were collected and divided into two age groups: middle-aged (42–63 years of age) and elderly (69–90 years of age) with ten males and ten females in each group (n = 10). Micro-cores of bone tissue from both secondary osteons and interstitial regions in the medial quadrant of the diaphysis were extracted using a custom-modified, computer-controlled milling machine. The bone specimens were then analyzed using high performance liquid chromatography to determine the effects of age and gender on the concentration of mature, enzymatic crosslinks (hydroxylysyl-pyridinoline—HP and lysyl-pyridinoline—LP) and a non-enzymatic crosslink (pentosidine—PE) at these two microstructural sites. The results indicate that age has a significant effect on the concentration of LP and PE, while gender has a significant effect on HP and LP. In addition, the concentration of the crosslinks in the secondary osteons is significantly different from that in the interstitial bone regions. These results suggest that the amount of non-enzymatic crosslinking may increase while that of mature enzymatic crosslinking may decrease with age. Such changes could potentially reduce the inherent quality of the bone tissue in the elderly skeleton.     

Absence of Mycobacterium avium ss paratuberculosis-specific IS900 sequence in intestinal biopsy tissues of Indian patients with Crohn’s disease

Background and Objective  

The role of Mycobacterium avium ss paratuberculosis (MAP) in the etiopathology of Crohn’s disease (CD) remains controversial, because of conflicting reports demonstrating the presence of MAP-specific insertion sequence from intestinal biopsy tissues of patients clinically diagnosed for the disease. The present study was carried out to investigate the presence of MAP DNA in the intestinal tissues of CD patients to ascertain the relevance of MAP in Indian patients with CD.     

The organic solute transporter alpha-beta, Ostalpha-Ostbeta, is essential for intestinal bile acid transport and homeostasis

The apical sodium-dependent bile acid transporter (Asbt) is responsible for transport across the intestinal brush border membrane; however, the carrier(s) responsible for basolateral bile acid export into the portal circulation remains to be determined. Although the heteromeric organic solute transporter Ostalpha-Ostbeta exhibits many properties predicted for a candidate intestinal basolateral bile acid transporter, the in vivo functions of Ostalpha-Ostbeta have not been investigated. To determine the role of Ostalpha-Ostbeta in intestinal bile acid absorption, the Ostalpha gene was disrupted by homologous recombination in mice. Ostalpha(-/-) mice were physically indistinguishable from wild-type mice. In everted gut sac experiments, transileal transport of taurocholate was reduced by >80% in Ostalpha(-/-) vs. wild-type mice; the residual taurocholate transport was further reduced to near-background levels in gut sacs prepared from Ostalpha(-/-)Mrp3(-/-) mice. The bile acid pool size was significantly reduced (>65%) in Ostalpha(-/-) mice, but fecal bile acid excretion was not elevated. The decreased pool size in Ostalpha(-/-) mice resulted from reduced hepatic Cyp7a1 expression that was inversely correlated with ileal expression of fibroblast growth factor 15 (FGF15). These data indicate that Ostalpha-Ostbeta is essential for intestinal bile acid transport in mice. Unlike a block in intestinal apical bile acid uptake, genetic ablation of basolateral bile acid export disrupts the classical homeostatic control of hepatic bile acid biosynthesis.     

Water sorption of CH3- and CF3-Bis-GMA based resins with additives

Objectives

To evaluate the effect of additives on the water sorption characteristics of Bis-GMA based copolymers and composites containing TEGDMA, CH₃Bis-GMA or CF₃Bis-GMA.

Material and methods

Fifteen experimental copolymers and corresponding composites were prepared combining Bis-GMA and TEGDMA, CH₃Bis-GMA or CF₃Bis-GMA, with aldehyde or diketone (24 and 32 mol%) totaling 30 groups. For composites, barium aluminosilicate glass and pyrogenic silica was added to comonomer mixtures. Photopolymerization was effected by 0.2 wt% each of camphorquinone and N,N-dimethyl-p-toluidine. Specimen densities in dry and water saturated conditions were obtained by Archimedes'' method. Water sorption and desorption were evaluated in a desorption-sorption-desorption cycle. Water uptake (%WU), water desorption (%WD), equilibrium solubility (ES; µg/mm³), swelling (f) and volume increase (%V) were calculated using appropriate equations.

Results

All resins with additives had increased %WU and ES. TEGDMA-containing systems presented higher %WU, %WD, ES, f and %V values, followed by resins based on CH₃Bis-GMA and CF₃Bis-GMA.

Conclusions

Aldehyde and diketone led to increases in the water sorption characteristics of experimental resins.