Cellular RNA Hubs: Friends and Foes of Plant Viruses

RNA granules are dynamic cellular foci that are widely spread in eukaryotic cells and play essential roles in cell growth and development, and immune and stress responses. Different types of granules can be distinguished, each with a specific function and playing a role in, for example, RNA transcription, modification, processing, decay, translation, and arrest. By means of communication and exchange of (shared) components, they form a large regulatory network in cells. Viruses have been reported to interact with one or more of these either cytoplasmic or nuclear granules, and act either proviral, to enable and support viral infection and facilitate viral movement, or antiviral, protecting or clearing hosts from viral infection. This review describes an overview and recent progress on cytoplasmic and nuclear RNA granules and their interplay with virus infection, first in animal systems and as a prelude to the status and current developments on plant viruses, which have been less well studied on this thus far.

The SUMO Conjugation Complex Self-Assembles into Nuclear Bodies Independent of SIZ1 and COP1

Attachment of the small ubiquitin-like modifier (SUMO) to substrate proteins modulates their turnover, activity, or interaction partners. However, how this SUMO conjugation activity concentrates the proteins involved and the substrates into uncharacterized nuclear bodies (NBs) remains poorly understood. Here, we characterized the requirements for SUMO NB formation and for their subsequent colocalization with the E3 ubiquitin ligase CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1), a master regulator of plant growth. COP1 activity results in degradation of transcription factors, which primes the transcriptional response that underlies elongation growth induced by darkness and high ambient temperatures (skoto- and thermomorphogenesis, respectively). SUMO conjugation activity alone was sufficient to target the SUMO machinery into NBs. Colocalization of these bodies with COP1 required, in addition to SUMO conjugation activity, a SUMO acceptor site in COP1 and the SUMO E3 ligase SAP and Miz 1 (SIZ1). We found that SIZ1 docks in the substrate-binding pocket of COP1 via two valine-proline peptide motifs, which represent a known interaction motif of COP1 substrates. The data reveal that SIZ1 physically connects COP1 and SUMO conjugation activity in the same NBs that can also contain the blue-light receptors CRYPTOCHROME 1 and CRYPTOCHROME 2. Our findings thus suggest that sumoylation stimulates COP1 activity within NBs. Moreover, the presence of SIZ1 and SUMO in these NBs explains how both the timing and amplitude of the high-temperature growth response is controlled. The strong colocalization of COP1 and SUMO in these NBs might also explain why many COP1 substrates are sumoylated.

Arabidopsis TCP Transcription Factors Interact with the SUMO Conjugating Machinery in Nuclear Foci

In Arabidopsis more than 400 proteins have been identified as SUMO targets, both in vivo and in vitro. Among others, transcription factors (TFs) are common targets for SUMO conjugation. Here we aimed to exhaustively screen for TFs that interact with the SUMO machinery using an arrayed yeast two-hybrid library containing more than 1,100 TFs. We identified 76 interactors that foremost interact with the SUMO conjugation enzyme SCE1 and/or the SUMO E3 ligase SIZ1. These interactors belong to various TF families, which control a wide range of processes in plant development and stress signaling. Amongst these interactors, the TCP family was overrepresented with several TCPs interacting with different proteins of the SUMO conjugation cycle. For a subset of these TCPs we confirmed that the catalytic site of SCE1 is essential for this interaction. In agreement, TCP1, TCP3, TCP8, TCP14, and TCP15 were readily SUMO modified in an E. coli sumoylation assay. Strikingly, these TCP-SCE1 interactions were found to redistribute these TCPs into nuclear foci/speckles, suggesting that these TCP foci represent sites for SUMO (conjugation) activity.

Resolution of long-standing necrobiosis lipoidica diabeticorum (NLD) lesion after restoration of euglycemia following successful pancreas after kidney (PAK) transplantation: a case report

Necrobiosis lipoidica diabeticorum (NLD) is an inflammatory skin disorder of unknown cause which can be seen in patients with diabetes mellitus. Various treatments, including immunosuppressive agents have been tried, without consistent efficacy. NLD is generally thought not to correlate well with tight diabetic control. Pancreas transplantation is the only widely and clinically used treatment that restores euglycemia in type I diabetic recipients. We report a case of resolution of NLD that had been unchanged for decades before pancreas after kidney transplantation. Another unique aspect of our case was that immunosuppression was discounted as a confounding factor, because the patient had been exposed to the same antirejection regimen for 3 years preceding the pancreas transplantation.

Oral paricalcitol reduces the prevalence of posttransplant hyperparathyroidism: results of an open label randomized trial

Postkidney transplant hyperparathyroidism is a significant problem. Vitamin D receptor agonists are known to suppress parathyroid hormone (PTH) secretion. We examined the effect of oral paricalcitol on posttransplant secondary hyperparathyroidism by conducting an open label randomized trial in which 100 incident kidney transplant recipients were randomized 1:1 to receive oral paricalcitol, 2 μg per day, for the first year posttransplant or no additional therapy. Serial measurements of serum PTH, calcium and bone alkaline phosphatase, 24-h urine calcium and bone density were performed. The primary endpoint was the frequency of hyperparathyroidism 1-year posttransplant. Eighty-seven patients completed the trial. One-year posttransplant, 29% of paricalcitol-treated subjects had hyperparathyroidism compared with 63% of untreated patients (p = 0.0005). Calcium supplementation was discontinued in two control and 15 treatment patients due to mild hypercalcemia or hypercalcuria. Paricalcitol was discontinued in four patients due to hypercalcuria/hypercalcemia and in one for preference. Two subjects required decreasing the dose of paricalcitol to 1 μg daily. Hypercalcemia was asymptomatic and reversible. Incidence of acute rejection, BK nephropathy and renal function at 1 year were similar between groups. Moderate renal allograft fibrosis was reduced in treated patients. Oral paricalcitol is effective in decreasing posttransplant hyperparathyroidism and may have beneficial effects on renal allograft histology.

Serum D-dimer concentrations in nephrotic syndrome track with albuminuria, not estimated glomerular filtration rate

BACKGROUND

The nephrotic syndrome is associated with an increased risk of venous and arterial thrombosis. There are little published data on the distribution, interpretation or determinants of serum D-dimer levels in patients with the nephrotic syndrome. We aimed to describe this relationship.

METHODS

This was a cross-sectional study of 100 patients with the nephrotic syndrome. Multivariate linear regression was used to evaluate for independent predictors of elevated D-dimer levels. Patients were observed for a period of 2 years after the baseline measurement of D-dimer level to assess for subsequent clinically evident thrombosis.

RESULTS

On univariate linear regression, D-dimer elevation was associated with age in years β (95% CI) 0.02 (0.016, 0.03), log-transformed urinary protein:creatinine ratio in g/g 0.439 (0.32, 0.558) and inversely with serum albumin in g/l -0.05 (-0.073, -0.035) and estimated glomerular filtration rate (eGFR) in ml/min/1.73 m(2) -0.01 (-0.016, -0.003). On multivariate linear regression, age in years β (95% CI) 0.019 (0.012, 0.026), serum albumin in g/l -0.023 (-0.043, -0.003), and log-transformed urinary protein:creatinine ratio in g/g 0.266 (0.124, 0.408) were independently associated with elevated D-dimer levels.

CONCLUSION

D-dimer levels are commonly raised in the nephrotic syndrome in the absence of clinically evident thrombosis, and are independently associated with age, degree of proteinuria and serum albumin, but not with eGFR. Baseline levels of D-dimer did not predict subsequent episodes of clinically evident thrombosis after 2 years of follow-up.

Global SUMO Proteome Responses Guide Gene Regulation, mRNA Biogenesis, and Plant Stress Responses

Small Ubiquitin-like MOdifier (SUMO) is a key regulator of abiotic stress, disease resistance, and development in plants. The identification of >350 plant SUMO targets has revealed many processes modulated by SUMO and potential consequences of SUMO on its targets. Importantly, highly related proteins are SUMO-modified in plants, yeast, and metazoans. Overlapping SUMO targets include heat-shock proteins (HSPs), transcription regulators, histones, histone-modifying enzymes, proteins involved in DNA damage repair, but also proteins involved in mRNA biogenesis and nucleo-cytoplasmic transport. Proteomics studies indicate key roles for SUMO in gene repression by controlling histone (de)acetylation activity at genomic loci. The responsible heavily sumoylated transcriptional repressor complexes are recruited by plant transcription factors (TFs) containing an (ERF)-associated Amphiphilic Repression (EAR) motif. These TFs are not necessarily themselves a SUMO target. Conversely, SUMO acetylation (Ac) prevents binding of downstream partners by blocking binding of their SUMO-interaction peptide motifs to Ac-SUMO. In addition, SUMO acetylation has emerged as a mechanism to recruit specifically bromodomains. Bromodomains are generally linked with gene activation. These findings strengthen the idea of a bi-directional sumo-acetylation switch in gene regulation. Quantitative proteomics has highlighted that global sumoylation provides a dynamic response to protein damage involving SUMO chain-mediated protein degradation, but also SUMO E3 ligase-dependent transcription of HSP genes. With these insights in SUMO function and novel technical advancements, we can now study SUMO dynamics in responses to (a)biotic stress in plants.

Global SUMO Proteome Responses Guide Gene Regulation, mRNA Biogenesis, and Plant Stress Responses

Small Ubiquitin-like MOdifier (SUMO) is a key regulator of abiotic stress, disease resistance, and development in plants. The identification of >350 plant SUMO targets has revealed many processes modulated by SUMO and potential consequences of SUMO on its targets. Importantly, highly related proteins are SUMO-modified in plants, yeast, and metazoans. Overlapping SUMO targets include heat-shock proteins (HSPs), transcription regulators, histones, histone-modifying enzymes, proteins involved in DNA damage repair, but also proteins involved in mRNA biogenesis and nucleo-cytoplasmic transport. Proteomics studies indicate key roles for SUMO in gene repression by controlling histone (de)acetylation activity at genomic loci. The responsible heavily sumoylated transcriptional repressor complexes are recruited by plant transcription factors (TFs) containing an (ERF)-associated Amphiphilic Repression (EAR) motif. These TFs are not necessarily themselves a SUMO target. Conversely, SUMO acetylation (Ac) prevents binding of downstream partners by blocking binding of their SUMO-interaction peptide motifs to Ac-SUMO. In addition, SUMO acetylation has emerged as a mechanism to recruit specifically bromodomains. Bromodomains are generally linked with gene activation. These findings strengthen the idea of a bi-directional sumo-acetylation switch in gene regulation. Quantitative proteomics has highlighted that global sumoylation provides a dynamic response to protein damage involving SUMO chain-mediated protein degradation, but also SUMO E3 ligase-dependent transcription of HSP genes. With these insights in SUMO function and novel technical advancements, we can now study SUMO dynamics in responses to (a)biotic stress in plants.

Outcomes after simultaneous pancreas and kidney transplantation and the discriminative ability of the C-peptide measurement pretransplant among type 1 and type 2 diabetes mellitus

BACKGROUND

Earlier studies reporting outcomes after pancreas transplantation have included a combination of C-peptide cutoffs and clinical criteria to classify type 2 diabetes mellitus (T2DM). However, because the kidney is the major site for C-peptide catabolism, C-peptide is unreliable to discriminate the type of diabetes in patients with kidney disease.

METHODS

To improve the discriminative power and better classify the type of diabetes, we used a composite definition to identify T2DM: presence of C-peptide, negative glutamic acid decarboxylase antibody, absence of diabetic ketoacidosis, and use of oral hypoglycemics. Additionally among T2DM patients with end-stage renal disease (ESRD), body mass index of <30 kg/m(2) and use of <1 u/kg of insulin per day were selection criteria for suitablity for simultaneous pancreas and kidney transplantation (SPKT). We compared graft and patient survival between T1DM and T2DM after SPKT.

RESULTS

Our study cohort consisted of 80 patients, 10 of whom were assigned as T2DM based on our study criteria. Approximately 15% of patients with T1DM had detectable C-peptide. Cox regression survival analyses found no significant differences in allograft (pancreas and kidney) or patient survival between the 2 groups. The mean creatinine clearance at 1 year estimated by the modification of Diet in Renal Disease (MDRD) equation was not significantly different between the 2 groups. Among those with 1 year of follow-up, all patients with T2DM had glycosylate hemoglobin of <6.0 at 1 year versus 92% of those with T1DM.

CONCLUSION

SPKT should be considered in the therapeutic armamentarium for renal replacement in selected patients with T2DM and ESRD. Use of C-peptide measurements for ESRD patients can be misleading as the sole criterion to determine the type of diabetes.

Pilot study: association of traditional and genetic risk factors and new-onset diabetes mellitus following kidney transplantation

INTRODUCTION

New-onset diabetes mellitus, which occurs after kidney transplant and type 2 diabetes mellitus (T2DM), shares common risk factors and antecedents in impaired insulin secretion and action. Several genetic polymorphisms have been shown to be associated with T2DM. We hypothesized that transplant recipients who carry risk alleles for T2DM are "tipped over" to develop diabetes mellitus in the posttransplant milieu.

METHODS

We investigated the association of genetic and traditional risk factors present before transplantation and the development of new-onset diabetes mellitus after kidney transplantation (NODAT). Markers in 8 known T2DM-linked genes were genotyped using either the iPLEX assay or allelic discrimination (AD)-PCR in the study cohort testing for association with NODAT. We used univariate and multivariate logistic regression models for the association of pretransplant nongenetic and genetic variables with the development of NODAT.

RESULTS

The study cohort included 91 kidney transplant recipients with at least 1 year posttransplant follow-up, including 22 who developed NODAT. We observed that increased age, family history of T2DM, pretransplant obesity, and triglyceridemia were associated with NODAT development. In addition, we observed positive trends, although statistically not significant, for association between T2DM-associated genes and NODAT.

CONCLUSIONS

These findings demonstrated an increased NODAT risk among patient with a positive family history for T2DM, which, in conjunction with the observed positive predictive trends of known T2DM-associated genetic polymorphisms with NODAT, was suggestive of a genetic predisposition to NODAT.

Impact of subclinical inflammation on the development of interstitial fibrosis and tubular atrophy in kidney transplant recipients

Our aim was to study the impact of subclinical inflammation on the development of interstitial fibrosis and tubular atrophy (IF/TA) on a 1-year protocol biopsy in patients on rapid steroid withdrawal (RSW). A total of 256 patients were classified based on protocol biopsy findings at months 1 or 4. Group 1 is 172 patients with no inflammation, group 2 is 50 patients with subclinical inflammation (SCI), group 3 is 19 patients with subclinical acute rejection (SAR) and group 4 is 15 patients with clinical acute rejection (CAR). On the 1-year biopsy, more patients in group 2 (SCI) (34%, p = 0.004) and group 3 (SAR) (53%, p = 0.0002), had an IF/TA score > 2 compared to group 1 (control) (15%). IF/TA was not increased in group 4 (CAR) (20%). The percent with IF/TA score > 2 and interstitial inflammation (Banff i score > 0) was higher in group 2 (16%, p = 0.004) and group 3 (37%, p < 0.0001) compared to group 1 (3%). In a multivariate analysis, patients in groups 2 or 3 had a higher risk of IF/TA score > 2 on the 1-year biopsy (OR 6.62, 95% CI 2.68-16.3). We conclude that SCI and SAR increase the risk of developing IF/TA in patient on RSW.

Deceased donor kidney transplantation from donors with acute renal failure due to rhabdomyolysis

With the current shortage of solid organs for transplant, the transplant community continues to look for ways to increase the number of organ donors, including extending the criteria for donation. In rhabdomyolysis, the byproducts of skeletal muscle breakdown leak into the circulation resulting in acute renal failure in up to 30% of patients. In nonbrain dead patients, this condition is reversible and most patients recover full renal function. Seven potential donors had rhabdomyolysis with acute renal failure as evidenced by the presence of urine hemoglobin, plasma creatinine kinase levels of greater than five times the normal and elevated creatinine. One donor required dialysis. At our institution, 10 kidneys were transplanted from the seven donors. Two grafts had immediate function, five grafts experienced slow graft function and three grafts had delayed graft function requiring hemodialysis. At a mean of 8.7 months posttransplant (2.4-25.2 months), all patients have good graft function, are off dialysis and have a mean creatinine of 1.3 (0.7-1.8). In conclusion, our experience suggests that rhabdomyolysis with acute renal failure should not be a contraindication for donation, although recipients may experience slow or delayed graft function.

Diffuse parenchymal urine leak after kidney transplantation following degloving injury during donor nephrectomy

Laparoscopic donor nephrectomy can result in trauma to the kidney which may affect recipient graft function. In this case, the kidney sustained a complete degloving of the capsule during extraction. The kidney was transplanted and had immediate, good renal function, but postoperative course was complicated by a large urinoma that drained through the wound. Exploration was negative for a defined urine leak, but the surface of the denuded kidney was leaking a significant amount of unconcentrated urine. The patient was successfully treated with tissue glue treatment to the kidney surface and peritoneal window.

Acute Rejection Risk in Kidney Transplant Recipients on Steroid-Avoidance Immunosuppression Receiving Induction With Either Antithymocyte Globulin or Basiliximab

Immunosuppression with rapid discontinuation of corticosteroids, usually with induction therapy, is safe in kidney transplant recipients. In 89 patients, we induced immunosuppression with basiliximab or rabbit antithymocyte globulin (17 and 72 patients, respectively). Selection criteria for basiliximab were age (>or=65 years), history (malignancy; chronic infection), and type 1 diabetes mellitus (eligible for pancreas transplant). Steroids were administered through posttransplantation day 4 (five doses); maintenance immunosuppression was with tacrolimus and mycophenolate mofetil. At last follow-up (average, 286 days), most patients were steroid-free (antithymocyte globulin, 90%; basiliximab, 88%). Protocol biopsies were performed at 1, 4, and 12 months posttransplantation. The overall risk of biopsy-proven acute rejection was 12%. At 6 months posttransplantation, acute rejection-free survival was 93% for antithymocyte globulin, 65% for basiliximab (P<.001). Median time to biopsy-proven acute rejection was 27 and 71 days, respectively. The low incidence of biopsy-proven acute rejection with steroid-avoidance immunosuppression may be further reduced with antithymocyte globulin.

Steroid Avoidance Immunosuppression in Low-Risk Kidney Transplant Recipients

Recent clinical trials have documented the short-term safety of steroid avoidance (SA) in kidney transplant recipients. Since July 2003, we have used a SA immunosuppression protocol for low-risk kidney transplant recipients. Eligibility criteria are age > or = 18, primary transplant (living or deceased donor), and tacrolimus started by postoperative day 3. Recipients were excluded if peak/current PRA was >50%/20%, or if they had a positive flow crossmatch, or if they had the recent use of corticosteroids (<6 months). All recipients received induction with rabbit anti-thymocyte globulin, total dose 6 mg/kg, or basiliximab. Recipients received 5 daily doses of corticosteroid and mycophenolate mofetil 1 gm twice daily starting on the day of transplantation. Tacrolimus was started when the serum creatinine level decreased by 20%, or by postoperative day 3. The goal for trough tacrolimus levels was 10-15 ng/mL for the first month, 8-12 ng/mL for months 2-3, and 5-10 ng/mL after month 3. Protocol biopsies (bx) were performed at reperfusion, 1 month, 4 months, and 12 months. Ninety-four kidney transplantations were performed during the study period. Sixty-seven recipients (71%) were eligible and enrolled in SA. Characteristics of the 67 SA recipients: mean age, 53 years (range, 26-70); 41% female; 67% Caucasian; 24% Hispanic; 15% African American; and 5% Native American. Also, 77% received a living donor kidney. The mean follow-up was 180 days (range, 10-360). At last follow-up, 91% remained steroid-free. Biopsy-proven acute rejection (BPAR) occurred in 5 recipients (7.5%). Three recipients (4.5%) had clinical BPAR and 2 had subclinical. One recipient died with pneumonia 4 months following transplantation. Posttransplantation diabetes mellitus (PTDM) occurred in 2 (5%) of 38 recipients. In the initial 41 recipients, 27 had protocol bx at 1 month and 13 at 4 months available for analysis. Chronic allograft nephropathy (CAN) was present on protocol bx in 48% at 1 month and 69% at 4 month. Actuarial (Kaplan-Meier method) patient and graft survival rates at 351 days were 97.8% and 96.8%, respectively. SA with anti-thymocyte globulin induction in low-immunologic risk kidney transplant recipients is safe and is associated with a low risk of BPAR. The incidence of PTDM appears to be lower.

The fall, recovery, orbit, and composition of the Tagish Lake meteorite: a new type of carbonaceous chondrite

The preatmospheric mass of the Tagish Lake meteoroid was about 200,000 kilograms. Its calculated orbit indicates affinity to the Apollo asteroids with a semimajor axis in the middle of the asteroid belt, consistent with a linkage to low-albedo C, D, and P type asteroids. The mineralogy, oxygen isotope, and bulk chemical composition of recovered samples of the Tagish Lake meteorite are intermediate between CM and CI meteorites. These data suggest that the Tagish Lake meteorite may be one of the most primitive solar system materials yet studied.

Antiatherosclerotic activity of inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase in cholesterol-fed rabbits: a biochemical and morphological evaluation

Atherosclerotic lesion development was assessed in the thoracic aorta and chronically denuded iliac-femoral artery of hypercholesterolemic New Zealand White rabbits using inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase which have previously been shown to possess varying degrees of hepatoselectivity in rats. Atorvastatin, previously known as CI-981 (2.5 mg/kg), PD135022 (1.0 mg/kg), simvastatin (2.5 mg/kg), lovastatin (2.5 mg/kg), PD134965 (1.0 mg/kg), pravastatin (2.5 mg/kg) and BMY22089 (2.5 mg/kg) were added to a 0.5% cholesterol, 3% peanut, 3% coconut oil diet and fed for 8 weeks. Although reductions in plasma total cholesterol of 27% to 60%, VLDL-cholesterol of 31% to 71% and plasma total cholesterol exposure of 37% to 43% were obtained, no correlation between these parameters and vascular lipid content, lesion size or monocyte-macrophage content was noted. Iliac-femoral lipid content was unchanged; however, atorvastatin and simvastatin significantly reduced the cholesterol content of the thoracic aorta by 45%-62%. Atorvastatin and PD135022 reduced the size of the iliac-femoral lesion by 67% and monocyte-macrophage content by 72%. Simvastatin, lovastatin and PD134965 decreased the monocyte-macrophage content; however, lesion size was unchanged. Pravastatin and BMY22089 had no effect on lesion size or content. No compound significantly reduced the extent of thoracic aortic lesions. We concluded that changes in plasma lipids and lipoproteins noted with the various HMG-CoA reductase inhibitors did not account for the beneficial effect on atherosclerotic lesion development. The antiatherosclerotic potential of the HMG-CoA reductase inhibitors was compound-specific and clearly not a class effect.

Atherosclerotic lesion development in hypercholesterolemic Japanese quail following probucol treatment: a biochemical and morphologic evaluation

Probucol, a cholesterol-lowering agent which possesses antioxidant properties, was evaluated in hypercholesterolemic Japanese quail in order to assess the significance of antioxidant therapy on the development of atherosclerosis. Forty quail were fed a 0.5% cholesterol diet containing 0, 100, 200 or 500 mg kg-1 probucol for 2 months. At necropsy, plasma total and lipoprotein cholesterol and lipoprotein distribution were unchanged despite plasma probucol levels of 50 to 59 micrograms ml-1. The cholesteryl ester content of the liver and blood vasculature (brachiocephalic artery and aortic arch combined) was reduced by 33% and 62%, respectively, in animals given 500 mg kg-1 probucol. The vascular free cholesterol content was also reduced by 43 to 60% over the probucol dose range. Morphometric analysis of the brachiocephalic artery revealed that probucol reduced the incidence of lesions containing esterase-positive cells from 62% in untreated animals to 26% and 13% in animals administered 200 and 500 mg kg-1 probucol, respectively. No difference in mean wall thickness or area of the bracheocephalic artery was noted between the groups. Thus, we conclude that probucol can blunt the cholesteryl ester and macrophage enrichment of atherosclerotic lesions and this activity appears to be mediated by the compound's antioxidant properties since the changes noted were seen in the absence of alterations in plasma total and lipoprotein cholesterol levels.

The relationship between the degree of dietary-induced hypercholesterolemia in the rabbit and atherosclerotic lesion formation

A biochemical, histologic and morphometric evaluation of spontaneous, diet-induced (thoracic aorta) and injury-induced (iliac-femoral) atherosclerotic lesions was performed in rabbits maintained on varying levels of dietary cholesterol. Rabbits were meal-fed a 3% peanut oil, 3% coconut oil diet containing 0%, 0.1%, 0.25%, 0.5%, 1.0%, 1.5% or 2.0% cholesterol for 9 weeks. Plasma total cholesterol exposure (area under cholesterol-time curve (TC-AUC)) increased diet-dependently over the course of the study. VLDL and LDL cholesterol (VLDL-C, LDL-C) comprised 41% and 55%, respectively, of the plasma total cholesterol at cholesterol levels > 700 mg/dl (TC-AUC > 31,868 mg day/dl) and both VLDL-C and LDL-C were linearly related to TC-AUC (r = 0.98). Plasma TC-AUC was linearly related to thoracic aortic cholesteryl ester (CE) content (r = 0.74) and thoracic aortic lesion coverage (r = 0.66). In the injury-induced iliac-femoral lesion, plasma TC-AUC was linearly related to both iliac-femoral CE content (r = 0.80) and macrophage/lesion ratio (r = 0.64). At plasma cholesterol levels greater than 700 mg/dl, CE content of the iliac-femoral lesion ranged from 35 to 69 micrograms/mg dry defatted tissue, > 75% of the lesions were fibrofoamy in nature and macrophage/lesion area ratio was 0.46 to 0.55 while lesion area remained constant. VLDL-C and LDL-C were highly correlated with the CE content of both thoracic and iliac-femoral lesions, thoracic aortic lesion coverage and macrophage/lesion area ratio (r = 0.86-0.99). We conclude that the composition, extent and type of atherosclerotic lesion induced in rabbits is dependent upon the overall plasma cholesterol exposure, VLDL and LDL cholesterol content and whether lesions are induced by diet alone or both diet and chronic endothelial injury. In addition, various stages of atherosclerotic lesion formation can be replicated in the rabbit by titrating the animal's overall plasma cholesterol exposure.

Inhibition of acyl-CoA cholesterol O-acyltransferase reduces the cholesteryl ester enrichment of atherosclerotic lesions in the Yucatan micropig

Atherosclerotic lesion development may be altered indirectly by regulating plasma cholesterol or directly by inhibition of acyl-CoA cholesterol O-acyltransferase (ACAT) within cells of the artery. Yucatan micropigs were meal-fed a 2% cholesterol, 8% peanut oil, 8% coconut oil purified diet for 1 month prior to administration of the potent, bioavailable ACAT inhibitor CI-976, and induction of atherosclerotic lesions by chronic endothelial damage. After 84-108 days of therapy, CI-976 decreased mean plasma VLDL-cholesterol 85-91% and cumulative VLDL-exposure (area under VLDL-time curve) by 65%. However, overall plasma total, LDL and HDL cholesterol and triglyceride levels were unchanged. CI-976 decreased liver cholesteryl ester (CE) content 65% without significantly affecting adrenal CE content. The CE content of the injured left femoral, left iliac and abdominal aorta and uninjured right femoral and iliac arteries and thoracic aorta was reduced 62-78% by CI-976. Systemic plasma CI-976 levels measured 24 h post-dose ranged from 2.26 to 4.05 micrograms/ml and significantly correlated with the reduction in both VLDL and vessel CE content. Thus, we conclude that inhibition of ACAT can blunt the cholesteryl ester enrichment of developing atherosclerotic lesions by preventing reesterification and storage of lipoprotein cholesterol within vascular cells and by reducing the plasma level and delivery to the arterial wall of such atherogenic lipoproteins as VLDL.

Antiatherosclerotic effects of antioxidants are lesion-specific when evaluated in hypercholesterolemic New Zealand white rabbits

Oxidative modification of LDL may represent an initiating event in the formation of monocyte-macrophage foam cells, a major cell present in fatty streaks and atherosclerotic fibrous plaques. Therefore, we studied the effect of such antioxidants as probucol (500 mg/kg) and vitamins E and C (500 mg/kg each) on the regression of induced iliac-femoral lesions and progression of naturally occurring thoracic aortic fatty streak lesions in hypercholesterolemic New Zealand White rabbits. Following an initial 9-week lesion induction phase, both therapies were evaluated for 8 weeks. Probucol lowered plasma cholesterol 47% while vitamins E and C had no effect on plasma cholesterol. Probucol decreased the cholesteryl ester (CE) content of the thoracic aorta by 31% without changing the thoracic aortic lesion coverage. Vitamins E and C decreased thoracic aortic CE content by 40% and lesion coverage by 46%. Neither probucol nor vitamins E and C altered the CE content, lesion size, or macrophage/lesion ratio of the iliac-femoral artery. Thus, we conclude that the effects of antioxidants are specific to the stage of atherosclerotic lesion development. Antioxidant therapy alters the progression and cholesteryl ester enrichment of diet-induced thoracic aortic fatty streaks but has no effect on the progression and/or regression of more complicated injury-induced iliac-femoral lesions.