Citations

The permeability of insulin (Ins), nerve growth factor (NGF), albumin (Alb), transferrin (Trf), and IgG across the blood-nerve barrier (BNB) and blood-brain barrier (BBB) in normal adult rats was quantified by measuring the (permeability coefficient x surface area) product (PS) with the i.v. bolus-injection technique in the cannulated brachial vein and artery using radioiodinated proteins. The PS values of the BNB for IgG and Alb were low: 0.079 +/- 0.029 x 10(-6) and 0.101 +/- 0.088 x 10(-6) ml.g-1.s-1, (mean +/- SD, respectively). The PS values for NGF and Trf were 16.1-fold and 25.5-fold higher than for Alb. The PS for Ins across the BNB was 33.190 +/- 2.053 x 10(-6) ml.g-1.s-1--a remarkable 329-fold increase compared with Alb. The PS values of the BBB for IgG and Alb in different brain regions were all low, from 0.028 +/- 0.017 to 0.151 +/- 0.035 x 10(-6) ml.g-1.s-1 (mean +/- SD). NGF and Trf had comparable PS values from 13- to 32-fold higher than for Alb, except for the brain stem, where the PS for Trf was 66-fold higher than for Alb. The mean PS for Ins across the BBB ranged from 15.78 +/- 5.45 x 10(-6) ml.g-1.s-1 for the cortex to 22.62 +/- 7.50 x 10(-6) ml.g-1.s-1 for the brain stem--again a remarkable 105- to 390-fold increase relative to Alb. Because reliable PS measurements were obtained for all proteins tested, the BBB and BNB cannot be considered impermeable to proteins--a concept that has plagued brain- and nerve-barrier research. The low PS values for IgG and Alb indicate low rates of transfer; however, Alb, in particular, is the major protein of endoneurial and ventricular fluid, which suggests that these PS values may be significant. Ins had the highest PS values, which likely reflect the mechanism of transport across the barriers--that is, receptor-mediated transport. Because NGF and Trf had PS values 13- to 66-fold higher than for Alb, whether this reflects receptor-mediated uptake, adsorptive-mediated transcytosis, or some other mechanism is unclear. That the PS values for NGF and Trf differ from Alb and IgG clearly suggests, however, a different uptake mechanism. Finally, the remarkably high PS values for Ins across the BBB and BNB identify this protein and its putative receptor on capillary endothelial cells as a potential target for drug delivery into the central and peripheral nervous systems.

The blood-nerve transfer of human plasma albumin glycated with D-glucose was investigated by measuring the permeability coefficient-surface area product (PS) of the blood-nerve barrier to radioiodinated albumin in normal adult rat sciatic nerve. Human albumin (ALB) from normal individuals, freshly isolated by CM-Affi-Gel Blue affinity chromatography, was glycated in vitro for 1, 3, 10, 19, and 30 weeks. Glycated ALB (gALB) was separated from the nonglycated form by boronate-affinity chromatography. The efficiency of this separation was assessed by chromatography of ALB glycated with [14C]glucose and by rechromatography of isolated ALB and gALB after radioiodination. The gALB was also shown to have a higher molecular weight and be completely separated from ALB after SDS/pore gradient electrophoresis in a Tris borate/EDTA buffer. After 1 week of glycation, the gALB PS was 2.2-fold greater than the ALB PS (0.724 +/- 0.063 x 10(-6) vs. 0.328 +/- 0.053 x 10(-6) ml.g-1.s-1; mean +/- SD; P less than 0.0001) and it increased with the time of glycation reaching a maximum value of 16.2-fold greater at 30 weeks (4.656 +/- 1.117 x 10(-6) vs. 0.288 +/- 0.042 x 10(-6) ml.g-1.s-1; mean +/- SD; P less than 0.0001). No change was observed in the residual endoneurial plasma volume. In addition, the PS of gALB isolated from patients with diabetic polyneuropathy was significantly increased (P less than 0.0001) compared to the PS for ALB isolated from the same patients. It is hypothesized that the increased permeability of gALB and presumably other glycated serum components across the blood-nerve barrier, as well as the observed quantitative increase in ALB, IgG, and IgM in sural nerve biopsies from patients with diabetic polyneuropathy contribute to the development of diabetic polyneuropathy over a prolonged period of time by mechanisms that might involve osmotic changes in the nerve microenvironment, direct toxic effects of glycated macromolecules on cells within the endoneurium, or nerve damage by classical immunological mechanisms due to trapping of glycated immunoglobulins within nerve.

The albumin (Alb), IgG, and IgM concentrations in the endoneurium of fascicular sural nerve biopsy samples were evaluated in controls (n = 9 or 10), diabetic patients without neuropathy (n = 6), and diabetic patients with polyneuropathy (n = 17 or 18). These values were significantly increased in diabetic patients with and without neuropathy when expressed both per endoneurial dry weight or endoneurial total protein compared to biopsy samples from healthy controls. When these concentrations, expressed per endoneurial total protein, were related to plasma concentrations similarly expressed, the resulting blood-nerve barrier (BNB) indices were significantly increased for Alb (6.1 times; P less than 0.00001), IgG (4.9 times; P = 0.00037), and IgM (2.7 times; P = 0.015). The diabetic patients without neuropathy (defined as having an index of pathology of greater than 0.65; a measure of the severity of the pathological abnormality based on morphological criteria) also had significant increases in two of these BNB indices that were intermediate between the diabetic neuropathy patients and controls (Alb, 3.9 times controls; P = 0.00002: IgG, 4.6 times controls; P = 0.00016: IgM, 1.8 times controls; not significant). No correlations were observed between the endoneurial concentrations of these plasma proteins or the BNB indices and the index of pathology, suggesting that these increases in endoneurial plasma proteins precede the pathologic alterations. The increased values for the diabetics in the absence of pathological abnormalities may prove useful in predicting neuropathic complications. The ratio of the IgG-BNB index to the Alb-BNB index was decreased 19%, and the ratio of the IgM-BNB index to the Alb-BNB index was decreased 56% in diabetic neuropathy patients compared to controls. Although the IgG and IgM concentrations are increased in the diabetic endoneurium, the Alb increase is greater and a mechanism other than size indiscriminate extravasation of plasma proteins, therefore, is suggested. Morphometric assessment of the endoneurial compartments, which would be expected to contain these plasma proteins, suggests that they are not altered in diabetic neuropathy; hence, it is hypothesized that the observed increase in endoneurial concentration of these plasma proteins results from altered transport through the endothelial or perineurial barrier, which supports an underlying vascular mechanism in the development of diabetic polyneuropathy.

Purpose The maximum tolerated dose (MTD) and the dose-limiting toxicities of EKB-569, a selective, irreversible inhibitor of the epidermal growth factor receptor (EGFR), when administered orally once daily on an intermittent-dose schedule (14 days of a 28-day cycle) or on a continuous-dose schedule (each day of a 28-day cycle), were determined in patients with advanced solid tumors. Patients and Methods Planned dose escalation was 25, 50, 75, 125, 175, and 225 mg. Pharmacokinetic sampling was performed on days 1 and 14 for the intermittent-dose cohort and on days 1 and 15 for the continuous-dose cohort. Results Thirty patients received a median of two cycles (range, one to 10 cycles) in the intermittent-dose cohort; 29 patients received a median of three cycles (range, one to eight cycles) in the continuous-dose cohort. Dose-limiting toxicity was grade 3 diarrhea, and the MTD was 75 mg EKB-569 per day for both cohorts. Other common toxicities included rash, nausea, and asthenia. Exposure to EKB-569 was dose proportional. At the MTD, the mean ± standard deviation terminal half-life was 21.7 ± 4.2 hours and peak concentration increased 1.2-fold from day 1 to day 14/15. No major antitumor responses were observed. However, one patient with non–small-cell lung cancer and one with cutaneous squamous cell carcinoma had stable disease for 33 and 24 weeks, respectively. Conclusion The MTD of once-daily oral EKB-569 is 75 mg. The tolerable toxicity profile and long half-life of this irreversible EGFR inhibitor warrant its further evaluation as a single agent and in combination with other drugs.

Abstract The NOF cost-effectiveness model, based on clinical risk factors and femoral neck aBMD, predicted overall fracture risk in a cohort of postmenopausal women followed for up to 22 years. Introduction: To assess the ability of a statistical model to predict long-term fracture risk for a population of postmenopausal women, we compared observed fractures to those predicted by the National Osteoporosis Foundation's (NOF) cost-effectiveness model. Materials and Methods: In this population-based study, 393 postmenopausal Rochester, MN, women had baseline measurements of femoral neck areal BMD (aBMD) and assessment of the clinical risk factors (personal fracture history, family history of osteoporotic fracture, low body weight, and smoking status) that were included in the NOF model. They were then followed prospectively for up to 22 years. Fractures were ascertained by periodic interview and review of community medical records. Standardized incidence ratios (SIRs) compared observed fractures to predicted numbers. Results: During 4782 person-years of follow-up, 212 women experienced 503 fractures, two-thirds of which were caused by moderate trauma. When undiagnosed (incidentally noted) vertebral and rib fractures were excluded, there was general concordance between observed and predicted fractures of the hip (SIR, 0.78; 95% CI, 0.56-1.01), distal forearm (SIR, 1.22; 95% CI, 0.86-1.68), spine (SIR, 0.76; 95% CI, 0.50-1.11), and all other sites combined (SIR, 1.18; 95% CI, 0.97-1.42). Fracture prediction by the NOF model was about as good after 10 years as it was earlier during follow-up. Conclusions: This study validates the ability of a statistical model based on femoral neck aBMD and common clinical risk factors to predict the actual occurrence of fractures in a cohort of postmenopausal white women.

Abstract Osteoporosis is widely viewed as a major public health concern, but the exact magnitude of the problem is uncertain and likely to depend on how the condition is defined. Noninvasive bone mineral measurements can be used to define a state of heightened fracture risk (osteopenia), or the ultimate clinical manifestation of fracture can be assessed (established osteoporosis). If bone mineral measurements more than 2 standard deviations below the mean of young normal women represent osteopenia, then 45% of white women aged 50 years and over have the condition at one or more sites in the hip, spine, or forearm on the basis of population-based data from Rochester, Minnesota. A smaller proportion is affected at each specific skeletal site: 32% have bone mineral values this low in the lumbar spine, 29% in either of two regions in the proximal femur, and 26% in the midradius. Although this overall estimate is substantial, some other serious chronic diseases are almost as common. More importantly, low bone mass is associated with adverse health outcomes, especially fractures. The lifetime risk of any fracture of the hip, spine, or distal forearm is almost 40% in white women and 13% in white men from age 50 years onward. If the enormous costs associated with these fractures are to be reduced, increased attention must be given to the design and implementation of control programs directed at this major health problem.

Abstract In a population-based, cross-sectional study, we related age-associated changes in vBMD and in bone structural parameters to circulating bioavailable estradiol and testosterone levels in men. Associations between these bone mass/structural parameters and sex steroid levels were progressively stronger with age. Our previously postulated “threshold” for skeletal estrogen deficiency was most evident at cortical sites. Introduction: Serum sex steroids, particularly estrogen levels, are associated with bone mass in men, and previous work has suggested that there may be a “threshold” bioavailable estradiol (bio E2) level below which the male skeleton becomes estrogen deficient. However, previous studies addressing this issue have exclusively used DXA, which cannot separate trabecular from cortical bone or provide information on bone geometry or structure. Materials and Methods: In an age-stratified population sample of 314 men (age, 22-91 years), we assessed volumetric BMD (vBMD) and bone geometry by QCT at the lumbar spine, femoral neck, distal radius, and distal tibia and related these to circulating bio E2 and bio testosterone (T) levels. Results: Compared with young men (age, 20-39 years), middle-aged men (age, 40-59 years) had significantly lower bio T (−26%, p < 0.001) and bio E2 (−9%, p = 0.038) levels, and these decreases were even greater in the elderly men (age ≥ 60 years, −60% and −38% for bio T and bio E2, respectively, p < 0.001 for both). Reflecting their intact gonadal status, vBMD/structural parameters were not related to sex steroid levels in young men, whereas bio E2 levels were associated consistently with vBMD and variably with bone geometric parameters in the elderly men; middle-aged men showed associations with bio E2 and bio T at some sites. At all cortical sites, vBMD was associated with bio E2 at low (<30 pM, R = 0.27-0.41, p < 0.05-0.001) but not high (≥30 pM, R = −0.003 to 0.12, p = not significant) levels; no such differences were evident at trabecular sites. Conclusions: In men, bio E2 is the most consistent predictor of vBMD and some bone geometric variables as assessed by QCT. We also extend our previous findings on a possible “threshold” for skeletal estrogen deficiency by showing that this is most evident for cortical sites.

Abstract We studied whether oophorectomy performed after menopause is associated with an increased risk of hip or vertebral fractures in 6295 Study of Osteoporotic Fractures participants. There was no association between postmenopausal oophorectomy and the risk of hip or vertebral fractures. Introduction: Bilateral oophorectomy after natural menopause has been associated with an increased risk of osteoporotic fractures, potentially because of a decline in serum estradiol and testosterone levels after the oophorectomy. We prospectively tested this hypothesis in the Study of Osteoporotic Fractures (SOF). Materials and Methods: We studied 6295 white women ⩾65 years of age participating in the SOF who were not taking estrogen therapy at baseline. Hip fracture analyses included 708 hip fractures; vertebral fracture analyses included 267 incident vertebral fractures. Baseline serum estradiol and free testosterone values were available in a small subset of participants. Results and Conclusion: There were no significant differences in age, weight, or BMD between the women who underwent postmenopausal oophorectomy (n = 583) and those who did not (n = 5712). Free testosterone levels were significantly lower among women who had a postmenopausal oophorectomy. A history of postmenopausal oophorectomy was not associated with an increased risk of hip (hazard ratio [HR] = 1.1; 95% CI = 0.9-1.5) or vertebral fracture (HR = 0.7; 95% CI = 0.5-1.2). The relationship between oophorectomy and hip fracture was not altered by adding serum estradiol level (HR = 1.3; 95% CI = 0.5-3.2) or serum free testosterone level (HR = 1.7; 95% CI = 0.8-3.7) to the model. In summary, postmenopausal oophorectomy was not associated with an increased risk of hip or vertebral fracture in this cohort. These results are in contrast to previous findings, suggesting that the relationship between postmenopausal oophorectomy and fractures is not fully elucidated and that incidental oophorectomy after menopause should still be considered carefully in each potential patient.