Importance of vascular changes in selective neurodegeneration with thiamine deficiency

Vitamin B1 in critically ill patients: needs and challenges

BACKGROUND

Thiamine has a crucial role in energy production, and consequently thiamine deficiency (TD) has been associated with cardiac failure, neurological disorders, oxidative stress (lactic acidosis and sepsis) and refeeding syndrome (RFS). This review aims to explore analytical methodologies of thiamine compound quantification and highlight similarities, variances and limitations of current techniques and how they may be relevant to patients.

CONTENT

An electronic search of Medline, PubMed and Embase databases for original articles published in peer-reviewed journals was conducted. MethodsNow was used to search for published analytical methods of thiamine compounds. Keywords for all databases included "thiamine and its phosphate esters", "thiamine methodology" and terms related to critical illness. Enquiries were also made to six external quality assurance (EQA) programme organisations for the inclusion of thiamine measurement.

SUMMARY

A total of 777 published articles were identified; 122 were included in this review. The most common published method is HPLC with florescence detection. Two of the six EQA organisations include a thiamine measurement programme, both measuring only whole-blood thiamine pyrophosphate (TPP). No standard measurement procedure for thiamine compound quantification was identified.

OUTLOOK

Overall, there is an absence of standardisation in measurement methodologies for thiamine in clinical care. Consequently, multiple variations in method practises are prohibiting the comparison of study results as they are not traceable to any higher order reference. Traceability of certified reference materials and reference measurement procedures is needed to provide an anchor to create the link between studies and help bring consensus on the clinical importance of thiamine.

Feline Cerebrovascular Disease: Clinical and Histopathologic Findings in 16 Cats

Sixteen cats with cerebrovascular disease confirmed via histology to be of nontraumatic and nonneoplastic origins are described. In addition, the anatomy of the arterial supply of the cat's brain is reviewed. It is suggested that this unique arterial design may influence the incidence of cerebrovascular accidents in this species. Of the 16 cats reviewed, seven cats had ischemic infarctions, five had hemorrhagic infarctions, and four were diagnosed with intracranial hemorrhage. The median age was 8 yr and 9.5 yr in cats with infarctions and intracranial hemorrhages, respectively. Clinical signs were severe, acute, consistent with the localization of the cerebrovascular lesion, and influenced by underlying pathology. Four cats with infarction showed lateralized neurologic signs. Four cats with infarctions were diagnosed with pulmonary disease antemortem and three cats had hyperthyroidism. Cerebrospinal fluid analysis and computed tomography scans were available in two cats. None of the infarctions were grossly visible. All cats with hemorrhagic infarcts had severe liver pathology and nephritis was identified in four cats. Hypoxia was a feature in four cats and one cat suffered cardiac failure. In conclusion, the clinical picture is influenced by the type of cerebrovascular disease, the localization of the intracranial lesions, and any underlying pathology.

Up-regulation of caveolin-1 and blood-brain barrier breakdown are attenuated by N-acetylcysteine in thiamine deficiency

Wernicke's encephalopathy is a cerebral metabolic disorder caused by thiamine (vitamin B1) deficiency (TD). Neuropathologic consequences of TD include region-selective neuronal cell loss and blood-brain barrier (BBB) breakdown. Caveolin-1 is involved in the regulation of tight junction proteins and BBB permeability, and is modulated by oxidative stress, a feature of vulnerable brain regions in TD. We hypothesized that TD-related oxidative stress alters BBB integrity via induction of the caveolin-1 pathway. TD was induced in C57BL6 mice by treatment with a thiamine-deficient diet and administration of the thiamine antagonist pyrithiamine, in the absence or presence of the antioxidant N-acetylcysteine (NAC). A significant and focal increase in both caveolin-1 gene and protein expression was detected in the thalamus of thiamine-deficient mice, concomitant with IgG extravasation. Reduction of oxidative stress by NAC, as shown by normalization of reduced glutathione levels and attenuation of endothelial heme oxygenase-1 and nitric oxide synthase expression, resulted in prevention of the up-regulation of caveolin-1 in TD. Normalization of caveolin-1 levels by NAC was accompanied by a reduction in BBB breakdown, indicated by decreased IgG extravasation, normalization of occludin levels and prevention of matrix metalloproteinase-9 up-regulation. These findings demonstrate a role for caveolin-1 in TD pathogenesis, and suggest that oxidative stress contributes to BBB alterations in TD via modulation of this pathway.

Accumulation of nuclear DNA damage or neuron loss: molecular basis for a new approach to understanding selective neuronal vulnerability in neurodegenerative diseases

According to a long-standing hypothesis, aging is mainly caused by accumulation of nuclear (n) DNA damage in differentiated cells such as neurons due to insufficient nDNA repair during lifetime. In line with this hypothesis it was until recently widely accepted that neuron loss is a general consequence of normal aging, explaining some degree of decline in brain function during aging. However, with the advent of more accurate procedures for counting neurons, it is currently widely accepted that there is widespread preservation of neuron numbers in the aging brain, and the changes that do occur are relatively specific to certain brain regions and types of neurons. Whether accumulation of nDNA damage and decline in nDNA repair is a general phenomenon in the aging brain or also shows cell-type specificity is, however, not known. It has not been possible to address this issue with the biochemical and molecular-biological methods available to study nDNA damage and nDNA repair. Rather, it was the introduction of autoradiographic methods to study quantitatively the relative amounts of nDNA damage (measured as nDNA single-strand breaks) and nDNA repair (measured as unscheduled DNA synthesis) on tissue sections that made it possible to address this question in a cell-type-specific manner under physiological conditions. The results of these studies revealed a formerly unknown inverse relationship between age-related accumulation of nDNA damage and age-related impairment in nDNA repair on the one hand, and the age-related, selective, loss of neurons on the other hand. This inverse relation may not only reflect a fundamental process of aging in the central nervous system but also provide the molecular basis for a new approach to understand the selective neuronal vulnerability in neurodegenerative diseases, particularly Alzheimer's disease.

CNS drug delivery: opioid peptides and the blood-brain barrier

Peptides are key regulators in cellular and intercellular physiological responses and possess enormous promise for the treatment of pathological conditions. Opioid peptide activity within the central nervous system (CNS) is of particular interest for the treatment of pain owing to the elevated potency of peptides and the centrally mediated actions of pain processes. Despite this potential, peptides have seen limited use as clinically viable drugs for the treatment of pain. Reasons for the limited use are primarily based in the physiochemical and biochemical nature of peptides. Numerous approaches have been devised in an attempt to improve peptide drug delivery to the brain, with variable results. This review describes different approaches to peptide design/modification and provides examples of the value of these strategies to CNS delivery of peptide drugs. The various modes of modification of therapeutic peptides may be amalgamated, creating more efficacious "hybrid" peptides, with synergistic delivery to the CNS. The ongoing development of these strategies provides promise that peptide drugs may be useful for the treatment of pain and other neurologically-based disease states in the future.