Transcobalamin 776C→G polymorphism is associated with peripheral neuropathy in elderly individuals with high folate intake.

BACKGROUND: The 776C→G polymorphism of the vitamin B-12 transport protein transcobalamin gene (TCN2) (rs1801198; Pro259Arg) is associated with a lower holotranscobalamin concentration in plasma. This effect may reduce the availability of vitamin B-12 to tissues even when vitamin B-12 intake is adequate. Clinical outcomes associated with vitamin B-12 insufficiency could potentially be worsened by high folate intake. OBJECTIVE: We determined the association of the TCN2 776C→G polymorphism and folate intake with peripheral neuropathy in elders with normal plasma concentrations of vitamin B-12. DESIGN: Participants in this cross-sectional study (n = 171) were from a cohort of community-based, home-bound elderly individuals aged ≥60 y who underwent an evaluation by physicians including an assessment for peripheral neuropathy. Participants were administered food-frequency and general health status questionnaires, anthropometric measurements were taken, and a fasting blood sample from each subject was collected. RESULTS: Odds of neuropathy were 3-fold higher for GG genotypes than for CC genotypes (OR: 3.33; 95% CI: 1.15, 9.64). When folate intake was >2 times the Recommended Dietary Allowance (800 µg), GG genotypes had 6.9-fold higher odds of neuropathy than CC genotypes (OR: 6.9; 95% CI: 1.31, 36.36). There was no difference between the genotypes in the odds of peripheral neuropathy when folate intake was ≤800 µg (OR: 1.5; 95% CI: 0.18, 12.33). CONCLUSION: The TCN2 776C→G polymorphism is associated with increased odds of peripheral neuropathy in the elderly, even with a normal vitamin B-12 status, especially if their folate intake is >2 times the Recommended Dietary Allowance.

Reaction field analysis and lipid bilayer location for lipophilic fluorophores.

Environment polarity can cause changes in absorbance or emission maxima, for a given fluorophore. This is termed solvatochromism. In this study semiempirical models of solvatochromic shifts are used to predict their lipid bilayer location. Four reaction field models are analyzed and compared, to provide the most accurate prediction of fluorophore solvatochromic shifts using a modified version of the Lippert equation. For curcumin, the reaction field of Block and Walker gave the strongest agreement between experimental and predicted values (r = 0.978, p < 0.0001). For aluminum phthalocyanine disulfonic acid (AlPcS2), the reaction field of Wertheim, based on statistical mechanics, gave the best agreement (r = 0.951, p = 0.001) only when dispersion forces and solute polarizability are considered. The results of these models are correlated to the Dimroth-Reichardt ET(30) solvent polarity scale used by Frimer and colleagues. Using the model predicted values, curcumin is estimated to be 1-1.2 nm from the phospholipid-water interface, in the acyl chain region of the lipid bilayer. AlPcS2 is predicted to be 0.7-0.9 nm from the interface, at the fatty acid carbonyl. This investigation provides semiempirical methods to efficiently link fluorophore solvatochromic shifts to a location in the lipid bilayer via reaction field models.

Continuous exposure to low amplitude extremely low frequency electrical fields characterizing the vascular streaming potential alters elastin accumulation in vascular smooth muscle cells.

In normal development and pathology, the vascular system depends on complex interactions between cellular elements, biochemical molecules, and physical forces. The electrokinetic vascular streaming potential (EVSP) is an endogenous extremely low frequency (ELF) electrical field resulting from blood flowing past the vessel wall. While generally unrecognized, it is a ubiquitous electrical biophysical force to which the vascular tree is exposed. Extracellular matrix elastin plays a central role in normal blood vessel function and in the development of atherosclerosis. It was hypothesized that ELF fields of low amplitude would alter elastin accumulation, supporting a link between the EVSP and the biology of vascular smooth muscle cells. Neonatal rat aortic smooth muscle cell cultures were exposed chronically to electrical fields characteristic of the EVSP. Extracellular protein accumulation, DNA content, and electron microscopic (EM) evaluation were performed after 2 weeks of exposure. Stimulated cultures showed no significant change in cellular proliferation as measured by the DNA concentration. The per-DNA normalized protein in the extracellular matrix was unchanged while extracellular elastin accumulation decreased 38% on average. EM analysis showed that the stimulated cells had a 2.85-fold increase in mitochondrial number. These results support the formulation that ELF fields are a potential factor in both normal vessel biology and in the pathogenesis of atherosclerotic diseases including heart disease, stroke, and peripheral vascular disease.

A photodependent switch of liposome stability and permeability.

Liposomes offer a method to encapsulate high concentrations of a drug, protecting the therapeutic upon in vivo administration. With an appropriate mechanism to manipulate lipid bilayer permeability, liposomes have the potential to deliver encapsulated drugs in a spatially and temporally controlled manner. In this investigation, the photosensitizer aluminum phthalocyanine disulfonic acid (AlPcS(2)) is identified as a modulator of the colloidal properties of liposomes. AlPcS(2) adsorption to liposomes stabilizes lipid bilayers and reduces permeability. Spectroscopic data suggests that AlPcS(2) interacts with the phospholipid to increase lipid bilayer stability. In the presence of AlPcS(2), the liposome permeability was five times lower than that without the photosensitizer. This results in more stable liposome systems that contain higher doses of the encapsulated material for longer. Then, upon irradiation of the AlPcS(2)-liposome system with tissue penetrating red light, lipid bilayer permeability increases 10-fold over the baseline. The release is shown to be a singlet oxygen mediated process, due to the type II photodynamic action of AlPcS(2). It is concluded that this activity provides a novel photorelease mechanism for liposome mediated drug delivery.

Electric fields caused by blood flow modulate vascular endothelial electrophysiology and nitric oxide production.

Endothelial cells are exposed to a ubiquitous, yet unexamined electrical force caused by blood flow: the electrokinetic vascular streaming potential (EVSP). In this study, the hypothesis that extremely low frequency (ELF) electric fields parameterized by the EVSP have significant biological effects on endothelial cell properties was studied by measuring membrane potential and nitric oxide production under ELF stimulation between 0 and 2 Hz and 0-6.67 V/m. Using membrane potential and nitric oxide sensitive fluorescent dyes, bovine aortic endothelial cells (BAECs) in culture were studied in the presence and absence of EVSP-modeled electric fields. The transmembrane potential of BAECs was shown to depolarize between 1 and 7 mV with a strong dependency on both the magnitude and frequency of the isolated ELF field. The findings also support a field interaction with a frequency-dependent tuning curve. The ELF field complexly modulates the nitric oxide response to adenosine triphosphate stimulation with potentiation seen with up to a sevenfold increase. This potentiation was also frequency and magnitude dependent. An early logarithmic phase of NO production is enhanced in a field strength-dependent manner, but the ELF field does not modify a later exponential phase. This study shows that using electric fields on the order of those generated by blood flow influences the essential biology of endothelial cells. The inclusion of ELF electric fields in the paradigm of vascular biology may create novel opportunities for advancing both the understanding and therapies for treatment of vascular diseases.

Phase-amplitude investigation of spontaneous low-frequency oscillations of cerebral hemodynamics with near-infrared spectroscopy: a sleep study in human subjects.

We have investigated the amplitude and phase of spontaneous low-frequency oscillations (LFOs) of the cerebral deoxy- and oxy-hemoglobin concentrations ([Hb] and [HbO]) in a human sleep study using near-infrared spectroscopy (NIRS). Amplitude and phase analysis was based on the analytic signal method, and phasor algebra was used to decompose measured [Hb] and [HbO] oscillations into cerebral blood volume (CBV) and flow velocity (CBFV) oscillations. We have found a greater phase lead of [Hb] vs. [HbO] LFOs during non-REM sleep with respect to the awake and REM sleep states (maximum increase in [Hb] phase lead: ~π/2). Furthermore, during non-REM sleep, the amplitudes of [Hb] and [HbO] LFOs are suppressed with respect to the awake and REM sleep states (maximum amplitude decrease: 87%). The associated cerebral blood volume and flow velocity oscillations are found to maintain their relative phase difference during sleep, whereas their amplitudes are attenuated during non-REM sleep. These results show the potential of phase-amplitude analysis of [Hb] and [HbO] oscillations measured by NIRS in the investigation of hemodynamics associated with cerebral physiology, activation, and pathological conditions.

PHASE DIFFERENCE BETWEEN LOW-FREQUENCY OSCILLATIONS OF CEREBRAL DEOXY- AND OXY-HEMOGLOBIN CONCENTRATIONS DURING A MENTAL TASK.

Hemodynamic low-frequency (~0.1 Hz) spontaneous oscillations as detected in the brain by near-infrared spectroscopy have potential applications in the study of brain activation, cerebral autoregulation, and functional connectivity. In this work, we have investigated the phase lag between oscillations of cerebral deoxy- and oxy-hemoglobin concentrations in the frequency range 0.05-0.10 Hz in a human subject during a mental workload task. We have obtained a measure of such phase lag using two different methods: (1) phase synchronization analysis as used in the theory of chaotic oscillators and (2) a novel cross-correlation phasor approach. The two methods yielded comparable initial results of a larger phase lag between low-frequency oscillations of deoxy- and oxy-hemoglobin concentrations during mental workload with respect to a control, rest condition.

Electrical stimulation of peripheral nerves induces optical responses via skeletal muscle kinematics.

We have previously reported an optical response in human subjects occurring at 100 ms following electrical stimulation of peripheral nerves. In the present study, an animal model has been created to directly investigate the myogenic components of the signal. In addition, experiments have been performed in human subjects to investigate the signal's neuroanatomical specificity, sensitivity to muscle motion, and spatial and spectral features. The results of this work suggest that the observed optical signal derives from stimulus-induced motion associated with muscle contraction and likely contains myological information of clinical value.

An improved method for mapping cerebrovascular reserve using concurrent fMRI and near-infrared spectroscopy with Regressor Interpolation at Progressive Time Delays (RIPTiDe).

Cerebrovascular reserve (CVR) reflects the compensatory dilatory capacity of cerebral vasculature to a dilatory stimulus. Blood oxygen-level dependent (BOLD) fMRI has been proven to be an effective imaging technique to obtain CVR maps when subjects perform CO(2) inhalation or a breath-holding (BH) task. Here we propose a novel way to process the fMRI data obtained during a blocked BH task by using simultaneously collected near-infrared spectroscopy (NIRS) data as regressors to estimate the vascular contribution to the BOLD signal. Six healthy subjects underwent a 6min 30s resting state (RS) fMRI scan, followed by a scan of the same duration with a blocked BH task (5 breath holds with 20s durations separated by ~50s of regular breathing). NIRS data were recorded from a probe over the subjects' right prefrontal area. For each scan, the time course of changes in total hemoglobin (Δ[tHb]) was calculated from the NIRS data, time shifted by various amounts, and resampled to the fMRI acquisition rate. Each shifted time course was used as regressor in a general linear model analysis. The maximum parameter estimate across all time shifts was calculated at all voxels in both the BH and RS scans, and then converted into signal percentage changes. The ratio of these signal changes generates a CVR map of the BH response, normalized to the resting state. The NIRS regressor method makes no assumptions about the shape (or presence) of the BH response, and allows direct, quantitative comparison of the vascular BOLD response to BH to the baseline map obtained in the resting state.

A novel three-dimensional tool for teaching human neuroanatomy.

Three-dimensional (3D) visualization of neuroanatomy can be challenging for medical students. This knowledge is essential in order for students to correlate cross-sectional neuroanatomy and whole brain specimens within neuroscience curricula and to interpret clinical and radiological information as clinicians or researchers. This study implemented and evaluated a new tool for teaching 3D neuroanatomy to first-year medical students at Boston University School of Medicine. Students were randomized into experimental and control classrooms. All students were taught neuroanatomy according to traditional 2D methods. Then, during laboratory review, the experimental group constructed 3D color-coded physical models of the periventricular structures, while the control group re-examined 2D brain cross-sections. At the end of the course, 2D and 3D spatial relationships of the brain and preferred learning styles were assessed in both groups. The overall quiz scores for the experimental group were significantly higher than the control group (t(85) = 2.02, P < 0.05). However, when the questions were divided into those requiring either 2D or 3D visualization, only the scores for the 3D questions were significantly higher in the experimental group (F1(,)85 = 5.48, P = 0.02). When surveyed, 84% of students recommended repeating the 3D activity for future laboratories, and this preference was equally distributed across preferred learning styles (χ² = 0.14, n.s.). Our results suggest that our 3D physical modeling activity is an effective method for teaching spatial relationships of brain anatomy and will better prepare students for visualization of 3D neuroanatomy, a skill essential for higher education in neuroscience, neurology, and neurosurgery.

Spectral and spatial dependence ofdiffuse optical signals in response toperipheral nerve stimulation.

Using non-invasive, near-infrared spectroscopy we have previously reported optical signals measured at or around peripheral nerves in response to their stimulation. Such optical signals featured amplitudes on the order of 0.1% and peaked about 100 ms after peripheral nerve stimulation in human subjects. Here, we report a study of the spatial and spectral dependence of the optical signals induced by stimulation of the human median and sural nerves, and observe that these optical signals are: (1) unlikely due to either dilation or constriction of blood vessels, (2) not associated with capillary bed hemoglobin, (3) likely due to blood vessel(s) displacement, and (4) unlikely due to fiber-skin optical coupling effects. We conclude that the most probable origin of the optical response to peripheral nerve stimulation is from displacement of blood vessels within the optically probed volume, as a result of muscle twitch in adjacent areas.

Diffuse optical signals in response to peripheral nerve stimulation reflect skeletal muscle kinematics.

Previously we have reported a near-infrared optical response in the region occupied by a peripheral nerve that is distal to the site of electrical stimulation of that peripheral nerve. This "intermediate" signal is vascular in nature but its biological origin not been elucidated. In the present study, an animal model of the signal has been created and our human studies expanded to directly investigate the contribution of non-artifactual vascular motion induced by muscle contraction to the biological origin of this signal. Under non-invasive conditions during stimulation of the exposed sciatic nerve of the Sprague-Dawley rat, optical responses are robust. These signals can be abolished both pharmacologically and surgically using methods that eliminate muscle motion while leaving the electrophysiological health of the nerve intact. In human studies, signals that are elicited on stimulation of nerves containing motor axons, both within and outside the predicted imaging volume of the spectrometer, have similar temporal characteristics of those previously observed. Moreover, stimulation of sensory nerves alone does not elicit an optical response. These results strongly suggest that the intermediate signals are derived from stimulus-induced muscle contraction (whether via an innervating nerve or by direct stimulation) causing translational vascular motion within the optically interrogated region.

Near-infrared signals associated with electrical stimulation of peripheral nerves.

We report our studies on the optical signals measured non-invasively on electrically stimulated peripheral nerves. The stimulation consists of the delivery of 0.1 ms current pulses, below the threshold for triggering any visible motion, to a peripheral nerve in human subjects (we have studied the sural nerve and the median nerve). In response to electrical stimulation, we observe an optical signal that peaks at about 100 ms post-stimulus, on a much longer time scale than the few milliseconds duration of the electrical response, or sensory nerve action potential (SNAP). While the 100 ms optical signal we measured is not a direct optical signature of neural activation, it is nevertheless indicative of a mediated response to neural activation. We argue that this may provide information useful for understanding the origin of the fast optical signal (also on a 100 ms time scale) that has been measured non-invasively in the brain in response to cerebral activation. Furthermore, the optical response to peripheral nerve activation may be developed into a diagnostic tool for peripheral neuropathies, as suggested by the delayed optical signals (average peak time: 230 ms) measured in patients with diabetic neuropathy with respect to normal subjects (average peak time: 160 ms).

Reversible posterior leukoencephalopathy syndrome after bevacizumab/FOLFIRI regimen for metastatic colon cancer.

OBJECTIVE: To describe a patient with reversible posterior leukoencephalopathy syndrome following the administration of bevacizumab (Avastin), a monoclonal antibody against vascular endothelial growth factor. DESIGN: Case report/literature review. SETTING: University hospital. PATIENT: A 52-year-old man receiving chemotherapy for stage IV rectal carcinoma. RESULTS: Clinical and radiographic evidence consistent with reversible posterior leukoencephalopathy syndrome was found following the administration of irinotecan hydrochloride, leucovorin calcium, and fluorouracil (FOLFIRI) regimen chemotherapy and bevacizumab. CONCLUSIONS: Reversible posterior leukoencephalopathy syndrome following treatment with angiogenesis modulators can occur. In addition to raising clinical suspicion in appropriate patients, this report may yield clues to the pathophysiologic underpinnings of reversible posterior leukoencephalopathy syndrome.

Fast optical signals in the peripheral nervous system.

We present a study of the near-infrared optical response to electrical stimulation of peripheral nerves. The sural nerve of six healthy subjects between the ages of 22 and 41 was stimulated with transcutaneous electrical pulses in a region located approximately 10 cm above the ankle. A two-wavelength (690 and 830 nm) tissue spectrometer was used to probe the same sural nerve below the ankle. We measured optical changes that peaked 60 to 160 ms after the electrical stimulus. On the basis of the strong wavelength dependence of these fast optical signals, we argue that their origin is mostly from absorption rather than scattering. From these absorption changes, we obtain oxy- and deoxy-hemoglobin concentration changes that describe a rapid hemodynamic response to electrical nerve activation. In five out of six subjects, this hemodynamic response is an increase in total (oxy+deoxy) hemoglobin concentration, consistent with a fast vasodilation. Our findings support the hypothesis that the peripheral nervous system undergoes neurovascular coupling, even though more data is needed to prove such hypothesis.