Repeated Mild Concussive Events Heighten the Vulnerability of Brain to Blast Exposure.

Mild concussive events without loss of consciousness are typically left untreated and can result in neurological abnormalities at later stages of life. No systematic studies have been carried out to determine the effect of concussion or repeated mild concussive episodes on brain vulnerability towards blast exposure. We have evaluated the effect of repeated mild concussive events on the vulnerability of brain to blast exposure using neurobehavioral functional assessments. Rats were subjected to either repeated mild concussive impacts (two impacts 1 week apart using a modified Marmarou weight drop model), a single blast exposure (19 psi using an advanced blast simulator), or a single blast exposure one day after the second mild concussive impact. Neurobehavioral changes were monitored using rotating pole test, open field exploration test, and novel object recognition test. Rotating pole test results indicated that vestibulomotor function was unaffected by blast or repeated mild concussive impacts, but significant impairment was observed in the blast exposed animals who had prior repeated mild concussive impacts. Novel object recognition test revealed short-term memory loss at 1 month post-blast only in rats subjected to both repeated mild concussive impacts and blast. Horizontal activity count, ambulatory activity count, center time and margin time legacies in the open field exploratory activity test indicated that only those rats exposed to both repeated mild concussive impacts and blast develop anxiety-like behaviors at both acute and sub-acute time-points. The results indicate that a history of repeated mild concussive episodes heightens brain vulnerability to blast exposure.

Blast Exposure Alters Synaptic Connectivity in the Mouse Auditory Cortex.

Blast exposure can cause auditory deficits that have a lasting, significant impact on patients. Although the effects of blast on auditory functions localized to the ear have been well documented, the impact of blast on central auditory processing is largely undefined. Understanding the structural and functional alterations in the central nervous system (CNS) associated with blast injuries is crucial for unraveling blast-induced pathophysiological pathways and advancing development of therapeutic interventions. In this study, we used electrophysiology in combination with optogenetics assay, proteomic analysis, and morphological evaluation to investigate the impairment of synaptic connectivity in the auditory cortex (AC) of mice following blast exposure. Our results show that the long-range functional connectivity between the medial geniculate nucleus (MGN) and AC was impaired in the acute phase of blast injury. We also identified impaired synaptic transmission and dendritic spine alterations within 7 days of blast exposure, which recovered at 28 days post-blast. Additionally, proteomic analysis identified a few differentially expressed proteins in the cortex that are involved in synaptic signaling and plasticity. These findings collectively suggest that blast-induced alterations in the sound signaling network in the auditory cortex may underlie hearing deficits in the acute and sub-acute phases after exposure to shockwaves. This study may shed light on the perturbations underlying blast-induced auditory dysfunction and provide insights into the potential therapeutic windows for improving auditory outcomes in blast-exposed individuals.

Cerebrospinal Fluid Levels of Lysophosphatidic Acids Can Provide Suitable Biomarkers of Blast-Induced Traumatic Brain Injury.

Blast-induced traumatic brain injury (bTBI) has been identified as the signature injury of Operation Iraqi Freedom and Operation Enduring Freedom. Although the incidence of bTBI increased significantly after the introduction of improvised explosive devices, the mechanism of the injury is still uncertain, which is negatively impacting the development of suitable countermeasures. Identification of suitable biomarkers that could aid in the proper diagnosis of and prognosis for both acute and chronic bTBI is essential since bTBI frequently is occult and may not be associated with overtly detectable injuries to the head. Lysophosphatidic acid (LPA) is a bioactive phospholipid generated by activated platelets, astrocytes, choroidal plexus cells and microglia and is reported to play major roles in stimulating inflammatory processes. The levels of LPA in the cerebrospinal fluid (CSF) have been reported to increase acutely after non-blast related brain injuries. In the present study, we have evaluated the utility of LPA levels measured in the CSF and plasma of laboratory rats as an acute and chronic biomarker of brain injury resulting from single and tightly coupled repeated blast overpressure exposures. In the CSF, many LPA species increased at acute time-points, returned to normal levels at 1 month, and increased again at 6 months and 1 year post-blast overpressure exposures. In the plasma, several LPA species increased acutely, returned to normal levels by 24 h, and were significantly decreased at 1 year post-blast overpressure exposures. These decreases in LPA species in the plasma were associated with decreased levels of lysophosphatidyl choline, suggesting a defective upstream biosynthetic pathway of LPAs in the plasma. Notably, the changes in LPA levels in the CSF (but not plasma) negatively correlated with neurobehavioral functions in these rats, suggesting that CSF levels of LPAs may provide a suitable biomarker of bTBI that reflects severity of injury.

Upregulation of multiple toll-like receptors in ferret brain after blast exposure: Potential targets for treatment.

Although blast-induced traumatic brain injury (bTBI) has been designated as the signature injury of recent combat operations, its precise pathological mechanism(s) has not been identified thus far. Prior preclinical studies on bTBI demonstrated acute neuroinflammatory cascades which are known to be contributing to neurodegeneration. Danger-associated chemical patterns are released from the injured cells, which activate non-specific pattern recognition receptors, such as toll-like receptors (TLRs) leading to increased expression of inflammatory genes and release of cytokines. Upregulation of specific TLRs in the brain has been described as a mechanism of injury in diverse brain injury models unrelated to blast exposure. However, the expression profile of various TLRs in bTBI has not been investigated thus far. Hence, we have evaluated the expression of transcripts for TLR1-TLR10 in the brain of a gyrencephalic animal model of bTBI. We exposed ferrets to tightly coupled repeated blasts and determined the differential expression of TLRs (TLR1-10) by quantitative RT-PCR in multiple brain regions at 4 hr, 24 hr, 7 days and 28 days post-blast injury. The results obtained indicate that multiple TLRs are upregulated in the brain at 4 hr, 24 hr, 7 days and 28 days post-blast. Specifically, upregulation of TLR2, TLR4 and TLR9 was noted in different brain regions, suggesting that multiple TLRs might play a role in the pathophysiology of bTBI and that drugs that can inhibit multiple TLRs might have enhanced efficacy to attenuate brain damage and thereby improve bTBI outcome. Taken together, these results suggest that several TLRs are upregulated in the brain after bTBI and participate in the inflammatory response and thereby provide new insights into the disease pathogenesis. Therefore, inhibition of multiple TLRs, including TLR2, 4 and 9, simultaneously might be a potential therapeutic strategy for the treatment of bTBI.

Soft-armor Vest Effectiveness and Intrathoracic Biomechanics in Rodents Exposed to Primary Blast.

The biomechanics and efficacy of personal protective equipment in mitigating injuries from blast overpressure remain unclear. The objectives of this study were to define intrathoracic pressures in response to blast wave (BW) exposure and biomechanically evaluate a soft-armor vest (SA) at diminishing these perturbations. Male Sprague-Dawley rats were instrumented with pressure sensors in the thorax and were exposed laterally to multiple exposures ranging from 33 to 108 kPa BW with SA and without SA. There were significant increases in rise time, peak negative pressure, and negative impulse in the thoracic cavity compared to the BW. Esophageal measurements were increased to a greater extent when compared to the carotid and the BW for all parameters (except positive impulse, which decreased). SA minimally altered the pressure parameters and energy content. This study establishes the relationship of external blast flow conditions and intra-body biomechanical responses in the thoracic cavity of rodents with and without SA.

Blast Exposure Dysregulates Nighttime Melatonin Synthesis and Signaling in the Pineal Gland: A Potential Mechanism of Blast-Induced Sleep Disruptions.

Blast-induced traumatic brain injury (bTBI) frequently results in sleep-wake disturbances. However, limited studies have investigated the molecular signaling mechanisms underlying these sleep disturbances, and potentially efficacious therapies are lacking. We investigated the levels of melatonin and genes involved in melatonin synthesis pathway in the pineal glands of Sprague Dawley rats exposed to single and tightly coupled repeated blasts during the night and daytime. Rats were exposed to single and tightly coupled repeated blasts using an advanced blast simulator. The plasma, cerebrospinal fluid (CSF), and pineal gland were collected at 6 h, 24 h, or 1 month postblast at two different time points: one during the day (1000 h) and one at night (2200 h). Differential expressions of genes involved in pineal melatonin synthesis were quantified using quantitative real-time polymerase chain reaction (qRT-PCR). Plasma and CSF melatonin levels were assessed using a commercial melatonin ELISA kit. The plasma and CSF melatonin levels showed statistically significant decreases at 6 h and 24 h in the blast-exposed rats euthanized in the night (in dim light), with no significant alterations noted in rats euthanized in the morning (daylight) at all three-time points. Blast-exposed rats showed statistically significant decreases in Tph1, Aanat, Asmt, and Mtnr1b mRNA levels, along with increased Tph2 mRNA, in the pineal gland samples collected at night at 6 h and 24 h. No significant changes in the mRNA levels of these genes were noted at 1 month. These findings imply that the melatonin circadian rhythm is disrupted following blast exposure, which may be a factor in the sleep disturbances that blast victims frequently experience.

The Neurobehavioral Effects of Buprenorphine and Meloxicam on a Blast-Induced Traumatic Brain Injury Model in the Rat.

Previous findings have indicated that pain relieving medications such as opioids and non-steroidal anti-inflammatory drugs (NSAIDs) may be neuroprotective after traumatic brain injury in rodents, but only limited studies have been performed in a blast-induced traumatic brain injury (bTBI) model. In addition, many pre-clinical TBI studies performed in rodents did not use analgesics due to the possibility of neuroprotection or other changes in cognitive, behavioral, and pathology outcomes. To examine this in a pre-clinical setting, we examined the neurobehavioral changes in rats given a single pre-blast dose of meloxicam, buprenorphine, or no pain relieving medication and exposed to tightly-coupled repeated blasts in an advanced blast simulator and evaluated neurobehavioral functions up to 28 days post-blast. A 16.7% mortality rate was recorded in the rats treated with buprenorphine, which might be attributed to the physiologically depressive side effects of buprenorphine in combination with isoflurane anesthesia and acute brain injury. Rats given buprenorphine, but not meloxicam, took more time to recover from the isoflurane anesthesia given just before blast. We found that treatment with meloxicam protected repeated blast-exposed rats from vestibulomotor dysfunctions up to day 14, but by day 28 the protective effects had receded. Both pain relieving medications seemed to promote short-term memory deficits in blast-exposed animals, whereas vehicle-treated blast-exposed animals showed only a non-significant trend toward worsening short-term memory by day 27. Open field exploratory behavior results showed that blast exposed rats treated with meloxicam engaged in significantly more locomotor activities and possibly a lesser degree of responses thought to reflect anxiety and depressive-like behaviors than any of the other groups. Rats treated with analgesics to alleviate possible pain from the blast ate more than their counterparts that were not treated with analgesics, which supports that both analgesics were effective in alleviating some of the discomfort that these rats potentially experienced post-blast injury. These results suggest that meloxicam and, to a lesser extent buprenorphine alter a variety of neurobehavioral functions in a rat bTBI model and, because of their impact on these neurobehavioral changes, may be less than ideal analgesic agents for pre-clinical studies evaluating these neurobehavioral responses after TBI.

Phosphorylated Neurofilament Heavy Chain in the Cerebrospinal Fluid Is a Suitable Biomarker of Acute and Chronic Blast-Induced Traumatic Brain Injury.

Blast-induced traumatic brain injury (bTBI) has been documented as a significant concern for both military and civilian populations in response to the increased use of improvised explosive devices. Identifying biomarkers that could aid in the proper diagnosis and assessment of both acute and chronic bTBI is in urgent need since little progress has been made towards this goal. Addressing this knowledge gap is especially important in military veterans who are receiving assessment and care often years after their last blast exposure. Neuron-specific phosphorylated neurofilament heavy chain protein (pNFH) has been successfully evaluated as a reliable biomarker of different neurological disorders, as well as brain trauma resulting from contact sports and acute stages of brain injury of different origin. In the present study, we have evaluated the utility of pNFH levels measured in the cerebrospinal fluid (CSF) as an acute and chronic biomarker of brain injury resulting from single and tightly coupled repeated blast exposures using experimental rats. The pNFH levels increased at 24 h, returned to normal levels at 1 month, but increased again at 6 months and 1 year post-blast exposures. No significant changes were observed between single and repeated blast-exposed groups. To determine whether the observed increase of pNFH in CSF corresponded with its levels in the brain, we performed fluorescence immunohistochemistry in different brain regions at the four time-points evaluated. We observed decreased pNFH levels in those brain areas at 24 h, 6 months, and 1 year. The results suggest that blast exposure causes axonal degeneration at acute and chronic stages resulting in the release of pNFH, the abundant neuronal cytoskeletal protein. Moreover, the changes in pNFH levels in the CSF negatively correlated with the neurobehavioral functions in the rats, reinforcing suggestions that CSF levels of pNFH can be a suitable biomarker of bTBI.

Blast Exposure Causes Long-Term Degeneration of Neuronal Cytoskeletal Elements in the Cochlear Nucleus: A Potential Mechanism for Chronic Auditory Dysfunctions.

Blast-induced auditory dysfunctions including tinnitus are the most prevalent disabilities in service members returning from recent combat operations. Most of the previous studies were focused on the effect of blast exposure on the peripheral auditory system and not much on the central auditory signal-processing regions in the brain. In the current study, we have exposed rats to single and tightly coupled repeated blasts and examined the degeneration of neuronal cytoskeletal elements using silver staining in the central auditory signal-processing regions in the brain at 24 h, 14 days, 1 month, 6 months, and 1 year. The brain regions evaluated include cochlear nucleus, lateral lemniscus, inferior colliculus, medial geniculate nucleus, and auditory cortex. The results obtained indicated that a significant increase in degeneration of neuronal cytoskeletal elements was observed only in the left and right cochlear nucleus. A significant increase in degeneration of neuronal cytoskeletal elements was observed in the cochlear nucleus at 24 h and persisted through 1 year, suggesting acute and chronic neuronal degeneration after blast exposure. No statistically significant differences were observed between single and repeated blasts. The localized degeneration of neuronal cytoskeletal elements in the cochlear nucleus suggests that the damage could be caused by transmission of blast shockwaves/noise through the ear canal and that use of suitable ear protection devices can protect against acute and chronic central auditory signal processing defects including tinnitus after blast exposure.

Repeated Low-Level Blast Acutely Alters Brain Cytokines, Neurovascular Proteins, Mechanotransduction, and Neurodegenerative Markers in a Rat Model.

Exposure to the repeated low-level blast overpressure (BOP) periodically experienced by military personnel in operational and training environments can lead to deficits in behavior and cognition. While these low-intensity blasts do not cause overt changes acutely, repeated exposures may lead to cumulative effects in the brain that include acute inflammation, vascular disruption, and other molecular changes, which may eventually contribute to neurodegenerative processes. To identify these acute changes in the brain following repeated BOP, an advanced blast simulator was used to expose rats to 8.5 or 10 psi BOP once per day for 14 days. At 24 h after the final BOP, brain tissue was collected and analyzed for inflammatory markers, astrogliosis (GFAP), tight junction proteins (claudin-5 and occludin), and neurodegeneration-related proteins (Aß40/42, pTau, TDP-43). After repeated exposure to 8.5 psi BOP, the change in cytokine profile was relatively modest compared to the changes observed following 10 psi BOP, which included a significant reduction in several inflammatory markers. Reduction in the tight junction protein occludin was observed in both groups when compared to controls, suggesting cerebrovascular disruption. While repeated exposure to 8.5 psi BOP led to a reduction in the Alzheimer's disease (AD)-related proteins amyloid-ß (Aß)40 and Aß42, these changes were not observed in the 10 psi group, which had a significant reduction in phosphorylated tau. Finally, repeated 10 psi BOP exposures led to an increase in GFAP, indicating alterations in astrocytes, and an increase in the mechanosensitive ion channel receptor protein, Piezo2, which may increase brain sensitivity to injury from pressure changes from BOP exposure. Overall, cumulative effects of repeated low-level BOP may increase the vulnerability to injury of the brain by disrupting neurovascular architecture, which may lead to downstream deleterious effects on behavior and cognition.

Pulmonary injury risk curves and behavioral changes from blast overpressure exposures of varying frequency and intensity in rats.

At present, there are no set guidelines establishing cumulative limits for blast exposure numbers and intensities in military personnel, in combat or training operations. The objective of the current study was to define lung injury, pathology, and associated behavioral changes from primary repeated blast lung injury under appropriate exposure conditions and combinations (i.e. blast overpressure (BOP) intensity and exposure frequency) using an advanced blast simulator. Male Sprague Dawley rats were exposed to BOP frontally and laterally at a pressure range of ~ 8.5-19 psi, for up to 30 daily exposures. The extent of lung injury was identified at 24 h following BOP by assessing the extent of surface hemorrhage/contusion, Hematoxylin and Eosin staining, and behavioral deficits with open field activity. Lung injury was mathematically modeled to define the military standard 1% lung injury threshold. Significant levels of histiocytosis and inflammation were observed in pressures ≥ 10 psi and orientation effects were observed at pressures ≥ 13 psi. Experimental data demonstrated ~ 8.5 psi is the threshold for hemorrhage/contusion, up to 30 exposures. Modeling the data predicted injury risk up to 50 exposures with intensity thresholds at 8 psi for front exposure and 6psi for side exposures, which needs to be validated further.

Blast-induced hearing impairment in rats is associated with structural and molecular changes of the inner ear.

Auditory dysfunction is the most prevalent injury associated with blast overpressure exposure (BOP) in Warfighters and civilians, yet little is known about the underlying pathophysiological mechanisms. To gain insights into these injuries, an advanced blast simulator was used to expose rats to BOP and assessments were made to identify structural and molecular changes in the middle/inner ears utilizing otoscopy, RNA sequencing (RNA-seq), and histopathological analysis. Deficits persisting up to 1 month after blast exposure were observed in the distortion product otoacoustic emissions (DPOAEs) and the auditory brainstem responses (ABRs) across the entire range of tested frequencies (4-40 kHz). During the recovery phase at sub-acute time points, low frequency (e.g. 4-8 kHz) hearing improved relatively earlier than for high frequency (e.g. 32-40 kHz). Perforation of tympanic membranes and middle ear hemorrhage were observed at 1 and 7 days, and were restored by day 28 post-blast. A total of 1,158 differentially expressed genes (DEGs) were significantly altered in the cochlea on day 1 (40% up-regulated and 60% down-regulated), whereas only 49 DEGs were identified on day 28 (63% up-regulated and 37% down-regulated). Seven common DEGs were identified at both days 1 and 28 following blast, and are associated with inner ear mechanotransduction, cytoskeletal reorganization, myelin development and axon survival. Further studies on altered gene expression in the blast-injured rat cochlea may provide insights into new therapeutic targets and approaches to prevent or treat similar cases of blast-induced auditory damage in human subjects.

Blast Exposure Leads to Accelerated Cellular Senescence in the Rat Brain.

Blast-induced traumatic brain injury (bTBI) is one of the major causes of persistent disabilities in Service Members, and a history of bTBI has been identified as a primary risk factor for developing age-associated neurodegenerative diseases. Clinical observations of several military blast casualties have revealed a rapid age-related loss of white matter integrity in the brain. In the present study, we have tested the effect of single and tightly coupled repeated blasts on cellular senescence in the rat brain. Isoflurane-anesthetized rats were exposed to either a single or 2 closely coupled blasts in an advanced blast simulator. Rats were euthanized and brains were collected at 24 h, 1 month and 1 year post-blast to determine senescence-associated-ß-galactosidase (SA-ß-gal) activity in the cells using senescence marker stain. Single and repeated blast exposures resulted in significantly increased senescence marker staining in several neuroanatomical structures, including cortex, auditory cortex, dorsal lateral thalamic nucleus, geniculate nucleus, superior colliculus, ventral thalamic nucleus and hippocampus. In general, the increases in SA-ß-gal activity were more pronounced at 1 month than at 24 h or 1 year post-blast and were also greater after repeated than single blast exposures. Real-time quantitative RT-PCR analysis revealed decreased levels of mRNA for senescence marker protein-30 (SMP-30) and increased mRNA levels for p21 (cyclin dependent kinase inhibitor 1A, CDKN1A), two other related protein markers of cellular senescence. The increased senescence observed in some of these affected brain structures may be implicated in several long-term sequelae after exposure to blast, including memory disruptions and impairments in movement, auditory and ocular functions.

Antibodies Against Lysophosphatidic Acid Protect Against Blast-Induced Ocular Injuries.

Exposure to blast overpressure waves is implicated as the major cause of ocular injuries and resultant visual dysfunction in veterans involved in recent combat operations. No effective therapeutic strategies have been developed so far for blast-induced ocular dysfunction. Lysophosphatidic acid (LPA) is a bioactive phospholipid generated by activated platelets, astrocytes, choroidal plexus cells, and microglia and is reported to play major roles in stimulating inflammatory processes. The levels of LPA in the cerebrospinal fluid have been reported to increase acutely in patients with traumatic brain injury (TBI) as well as in a controlled cortical impact (CCI) TBI model in mice. In the present study, we have evaluated the efficacy of a single intravenous administration of a monoclonal LPA antibody (25 mg/kg) given at 1 h post-blast for protection against injuries to the retina and associated ocular dysfunctions. Our results show that a single 19 psi blast exposure significantly increased the levels of several species of LPA in blood plasma at 1 and 4 h post-blast. The anti-LPA antibody treatment significantly decreased glial cell activation and preserved neuronal cell morphology in the retina on day 8 after blast exposure. Optokinetic measurements indicated that anti-LPA antibody treatment significantly improved visual acuity in both eyes on days 2 and 6 post-blast exposure. Anti-LPA antibody treatment significantly increased rod photoreceptor and bipolar neuronal cell signaling in both eyes on day 7 post-blast exposure. These results suggest that blast exposure triggers release of LPAs, which play a major role promoting blast-induced ocular injuries, and that a single early administration of anti-LPA antibodies provides significant protection.

Long-Term Effects of Blast Exposure: A Functional Study in Rats Using an Advanced Blast Simulator.

Anecdotal observations of blast victims indicate that significant neuropathological and neurobehavioral defects may develop at later stages of life. To pre-clinically model this phenomenon, we have examined neurobehavioral changes in rats up to 1 year after exposure to single and tightly coupled repeated blasts using an advanced blast simulator. Neurobehavioral changes were monitored at acute, sub-acute, and chronic time-points using Morris water maze test of spatial learning and memory, novel object recognition test of short-term memory, open field exploratory activity as a test of anxiety/depression, a rotating pole test for vestibulomotor function, and a rotarod balance test for motor coordination. Single and repeated blasts resulted in significant functional deficits at both acute and chronic time-points. In most functional tests, rats exposed to repeated blasts performed more poorly than rats exposed to single blast. Interestingly, several functional deficits post-blast were most pronounced at 6 months and beyond. Significant neuromotor impairments occurred at early stages after blast exposure and the severity increased with repeated exposures. The novel object recognition testing revealed short-term memory deficits at 6 and 12 months post-blast. The water maze test revealed impairments at acute and chronic stages after blast exposure. The most substantial changes in the blast-exposed rats were observed with the center time and margin time legacies in the open field exploration test at 6, 9, and 12 months post-blast. Notably, these two outcome measures were minimally altered acutely, recovered during sub-acute stages, and were markedly affected during the chronic stages after blast exposures and may implicate development of chronic anxiety and depressive-like behaviors.

Defective methionine metabolism in the brain after repeated blast exposures might contribute to increased oxidative stress.

Blast-induced traumatic brain injury (bTBI) is one of the major disabilities in Service Members returning from recent military operations. The neurobiological underpinnings of bTBI, which are associated with acute and chronic neuropathological and neurobehavioral deficits, are uncertain. Increased oxidative stress in the brain is reported to play a significant role promoting neuronal damage associated with both brain injury and neurodegenerative disorders. In this study, brains of rats exposed to repeated blasts in a shock tube underwent untargeted profiling of primary metabolism by automatic linear exchange/cold injection GC-TOF mass spectrometry and revealed acute and sub-acute disruptions in the metabolism of the essential amino acid methionine and associated antioxidants. Methionine sulfoxide, the oxidized metabolite of methionine, showed a sustained increase in the brain after blast exposure which was associated with a significant decrease in cysteine, the amino acid derived from methionine. Glutathione, the antioxidant synthesized from cysteine, also concomitantly decreased as did the antioxidant ascorbic acid. Reductions in ascorbic acid were accompanied by increased levels of its oxidized metabolite, dehydroascorbic acid and other metabolites such as threonic acid, isothreonic acid, glycolic acid and oxalic acid. Fluorometric analysis of the brains showed acute and sub-acute increase in total reactive oxygen species. In view of the fundamental importance of glutathione in the brain as an antioxidant, including its role in the reduction of dehydroascorbic acid to ascorbic acid, the disruptions in methionine metabolism elicited by blast exposure might prominently contribute to neuronal injury by promoting increased and sustained oxidative stress.

Dose-response characteristics of high-viscosity hydroxypropylmethylcellulose in subjects at risk for the development of type 2 diabetes mellitus.

BACKGROUND: Hydroxypropylmethylcellulose (HPMC) is a modified cellulose fiber that creates a viscous solution in the gastrointestinal tract. The present study examined the dose-response characteristics of high-viscosity (HV)-HPMC consumption on postprandial glucose and insulin levels in men and women at increased risk for type 2 diabetes mellitus. METHODS: Subjects were a subset of participants in two trials with elevated peak postprandial glucose [>or=7.8 mmol/L (>or=140 mg/dL)] and body mass index (BMI) >or=27 kg/m(2). Subjects (n = 39) consumed breakfast meals containing 75 g of carbohydrate, each of which contained 1, 2, 4, or 8 g of HV-HPMC or a cellulose control in a randomized, double-blind manner. Each subject completed tests with control and two HV-HPMC doses. RESULTS: Peak glucose concentration was lower than control (all P < 0.01) following 2 g (10%), 4 g (18%), and 8 g (20%) of HV-HPMC. Peak insulin was also reduced (P < 0.01) following 2 g (32%), 4 g (35%), and 8 g (46%) of HV-HPMC doses versus control. Incremental areas for glucose from 0 to 120 min were reduced by 8-40% versus control but only reached significance for the 4-g and 8-g conditions, whereas incremental areas under the insulin curves were reduced by 14-53% (P < 0.01 for 2, 4, and 8 g of HV-HPMC). CONCLUSIONS: Among subjects at risk for type 2 diabetes mellitus, 1.0-8.0 g of HV-HPMC blunted postprandial glucose and insulin responses in a dose-dependent manner. Additional research is warranted to assess whether chronic consumption might retard the development or progression of glucose intolerance.

Hydroxypropylmethylcellulose and methylcellulose consumption reduce postprandial insulinemia in overweight and obese men and women.

Hydroxypropylmethylcellulose (HPMC) and methylcellulose (MC) are modified cellulose dietary fibers that generate viscous solutions in the gastrointestinal (GI) tract. This study assessed the effects of high viscosity (HV) HPMC, ultra-HV (UHV) HPMC, and medium viscosity MC on postprandial glucose and insulin responses in overweight and obese men and women (n = 50). After overnight fasts, subjects consumed 5 breakfast meals containing 75 g carbohydrate, each of which contained 1 of the following: 1 g HV-HPMC, 2 g HV-HPMC, 2 g UHV-HPMC, 4 g medium-viscosity MC or control (2 g cellulose). Test sequence was randomized and double-blind, except the MC test, which was last and single-blind (46 subjects completed all 5 tests). Glucose and insulin responses were determined pre-meal and for 120 min postprandially. Median (interquartile limits) peak glucose concentration was lower (P = 0.001) after the meal containing 2.0 g UHV-HPMC (7.1, 6.3-8.2 mmol/L) compared with the control meal (7.7, 6.6-8.7 mmol/L). The control did not differ from the other conditions for peak glucose or for any of the HPMC/MC conditions for glucose incremental areas under the curves (IAUC). Peak insulin was reduced (P < 0.05) for all HPMC/MC conditions compared with control. Insulin IAUC was lower than control (P < 0.001) after meals containing 2 g HV-HPMC, 2 g UHV-HPMC, and 4 g MC. GI symptoms did not differ among treatments. These findings indicate that HV-HPMC (1 and 2 g), UHV-HPMC (2 g), and MC (4 g) consumption reduced postprandial insulin excursions consistent with delayed glucose absorption.

High-viscosity hydroxypropylmethylcellulose blunts postprandial glucose and insulin responses.

OBJECTIVE: High-viscosity hydroxypropylmethylcellulose (HV-HPMC) is a modified cellulose fiber that produces a viscous gel in the gastrointestinal tract. Clinical trials demonstrate that consumption of HV-HPMC significantly lowers cholesterol, but limited information has been available on the influence of HV-HPMC on postprandial insulin and glucose responses. The objective of this investigation was to assess the influence of HV-HPMC on postprandial glucose and insulin responses in overweight and obese men and women. RESEARCH DESIGN AND METHODS: Participants were 31 overweight or obese men and women without diabetes who underwent three breakfast meal tests in random order, separated by > or = 72 h. Test meals containing 75 g carbohydrate plus 4 or 8 g HV-HPMC or control meals containing 8 g cellulose were delivered in a double-blind fashion. RESULTS: Peak glucose was significantly lower (P < 0.001) after both HV-HPMC-containing meals (7.4 mmol/l [4 g] and 7.4 mmol/l [8 g]) compared with the control meal (8.6 mmol/l). Peak insulin concentrations and the incremental areas for glucose and insulin from 0 to 120 min were also significantly reduced after both HV-HPMC doses versus control (all P < 0.01). CONCLUSIONS: These findings indicate that HV-HPMC consumption reduces postprandial glucose and insulin excursions, which may favorably alter risks for diabetes and cardiovascular disease.

Hypertonic resuscitation and blood coagulation: in vitro comparison of several hypertonic solutions for their action on platelets and plasma coagulation.

Resuscitation with hypertonic saline (HS) appears to aggravate bleeding in a model of uncontrolled hemorrhage [J. Trauma 28 (1988) 751; J. Trauma 29 (1989) 79; Arch. Surg. 127 (1992) 93]. This property may be related to the anticoagulant effects of HS on plasma clotting factors and platelets [J. Trauma 31 (1991) 8]. The hypothesis in this study is that a hypertonic solution can be developed that would not disturb the blood coagulation mechanism and could be used as an alternative to hypertonic saline.HS and four different 2400 mosM solutions containing monosaccharides and/or glycine were screened for their in vitro effects on plasma clotting times and platelets. Significant prolongations falling outside the normal range were detected in prothrombin time (PT) and thrombin rime (TT) when only 5% of the volume of normal plasma is HS. Platelet function as measured by extent of shape change (ESC) induced by ADP and aggregation induced by thrombin were also critically impaired by HS at a 5% dilution. All alternative solutions-hypertonic glucose, sorbitol, glycine, glucose/glycine, glucose/mannitol/glycine, sorbitol/glycine-caused a significantly reduced impairment in platelet function and the plasma coagulation system. Hypertonic glycine showed a unique ability to fully preserve the function and integrity of the plasma coagulation system. Considering the pre-deposition of the trauma patient to coagulopathy, administration of HS which clearly is a potent anticoagulant and anti-platelet risks further aggravating the coagulopathy. In contrast, hypertonic glycine preserves the blood coagulation mechanism and exhibits the potential for numerous therapeutic applications. Therefore, prompt evaluation of hypertonic glycine as a resuscitative fluid is highly desirable.