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Cranial Neuropathies II, III, IV, and VI
Published in Philip B. Gorelick, Fernando D. Testai, Graeme J. Hankey, Joanna M. Wardlaw, Hankey's Clinical Neurology, 2020
Tanyatuth Padungkiatsagul, Heather E. Moss
Optic neuritis is the presenting symptom in roughly half and eventually occurs in the majority of patients with NMO, an inflammatory central nervous system (CNS), distinct from MS that is related to AQP-4-IgG. It is important to maintain a high index of suspicion for NMO in patients with optic neuritis, since the morbidity and mortality rates are higher than for MS and the treatment is different.
Basics of CSF production
Published in Jyotirmay S. Hegde, Hemanth Vamanshankar, CSF Rhinorrhea, 2020
Hemanth Vamanshankar, Jyotirmay S Hegde
Transport of water, solutes, and ions in a bi-directional manner, in response to both hydraulic pressure and passive osmotic gradients, is controlled by aquaporins. These are highly selective of the molecule being transported, and at the same time provide rapid transport.35 Of the many aquaporins found (about 14 are identified), six are reported to be present in the brain.36–38 Permeability is specific to each of them; AQP3 and 9- permeable to small solutes and water; AQP8 to ions; and AQP 1, 4, 5 are water permeable. Of these, AQP1 is important in CSF formation; AQP9 in energy metabolism; AQP4 in the clearance of K+ released in neuronal activity and formation/resolution of brain edema.36 AQP4 channels move water by simple diffusion and vesicular transport – this is currently the most accepted theory of the function of AQP4 (Figure 2.2 C).39 Further, AQP4-rich areas like BBB and glia limitans at the subpial zones may also act as water channels for ISF-CSF drainage in extreme conditions.40 The discovery of aquaporins by Peter Agre, which resulted in his receiving a Nobel Prize in Chemistry in 2003, has led us to a greater understanding of biological fluid homeostasis and turnover.41
Aquaporin-Mediated Water Transport in Intrahepatic Bile Duct Epithelial Cells
Published in Gianfranco Alpini, Domenico Alvaro, Marco Marzioni, Gene LeSage, Nicholas LaRusso, The Pathophysiology of Biliary Epithelia, 2020
Anatoliy I. Masyuk, Nicholas F. LaRusso
The best-studied member of the AQP family is AQP1. When expressed in Xenopus oocytes, the unit permeability coefficient (pf) for AQP1 was found to be 1–16 x 10–14 cm3/s/channel.35 Permeability studies of AQP1 by stop flow measurements indicate extremely high flow rate (~3 × 109 water molecules per channel and per second). The permeability coefficients for water of the individual AQPs vary; some, such as AQPO, have relatively low water permeability (pf = 0.03–0.3 x 10–14 cm3/s/channel), whereas AQP4 has been reported to have a pf of15–24 x 10–14 cm3/s/channel.36 The functional relevance and molecular basis of the variability in the water transporting capacities of the individual AQPs is unclear. The curiously low water permeability exhibited by AQPO and AQP6 may reflect their need for activation.3 There may be additional factors that influence AQP water permeability, such as enhanced osmotic flow for AQP4 resulting from the assembly of AQP4 into large, closely packed OAPs and the physical state of membrane lipids.37
Plasma exchange for acute optic neuritis in neuromyelitis optica or neuromyelitis optica spectrum disorder: a systematic review
Published in Annals of Medicine, 2023
Yachinee Naphattalung, Wanicha Leetiratanai Chuenkongkaew, Niphon Chirapapaisan, Poramaet Laowanapiban, Supattra Sawangkul
The appearance of serum aquaporin-4 IgG antibody (AQP4-Ab) distinguishes NMO, which is an astrocytopathic disorder arising from MS and other demyelinating diseases [3]. After the disclosure of the association between AQP4-Ab and NMO, revised diagnostic criteria for NMO were promulgated in 2006 [4]. These criteria had a higher specificity than the preceding criteria of 1999 [2,4]. In 2015, new diagnostic criteria for NMOSD, namely, the International Consensus Diagnostic Criteria for NMOSD, were proposed by Wingerchuk et al. [5] Recurrent loss of vision from ON may initially or solely be found in NMOSD. Compared with MS, the prevalence of NMOSD is markedly higher among Asian than Western populations [4,6]. ON of NMOSD often manifests as severe visual loss and eventually results in complete blindness [4,7].
The aquaporin-4 water channel and updates on its potential as a drug target for Alzheimer’s disease
Published in Expert Opinion on Therapeutic Targets, 2023
Bret Silverglate, Xiaoyi Gao, Hannah P. Lee, Peter Maliha, George T. Grossberg
Until the discovery of aquaporins in 1992, the general question of how water crossed biological membranes remained a mystery. While researching the Rhesus factor, Peter Agre’s team at Johns Hopkins made the serendipitous discovery of what is now known as aquaporin-1 [3]. Agre was later awarded the Nobel Prize in Chemistry in 2003 for this work. AQP4 was discovered nearly simultaneously by Agre’s group at Johns Hopkins University and Verkman’s group at UCSF and was so named because it was the fourth aquaporin discovered. Unlike the three previously discovered, it was localized primarily in the central nervous system (CNS) of rats, with only minute amounts found in the lungs and kidneys [4]. Thus, AQP4 was hypothesized to be a primary regulator of water balance in the CNS. Although there had been some previous descriptions of aquaporins in the CNS, Agre’s paper established the existence of a separate one located near-exclusively in the CNS [5,6].
Disorders of vision in multiple sclerosis
Published in Clinical and Experimental Optometry, 2022
Roshan Dhanapalaratnam, Maria Markoulli, Arun V Krishnan
Neuromyelitis optica spectrum disorder (NMOSD) is an inflammatory demyelinating CNS disease that may present similarly to MS (Table 1). From a diagnostic perspective, the most notable feature of NMOSD is the presence of antibodies to aquaporin 4 (AQP4) IgG antibody positive in ~80% of patients.57 AQP4 is a water channel protein found in high concentrations in grey matter of the spinal cord, the blood brain barrier, periaqueductal and periventricular regions.57 Of the AQP4 antibody negative patients, ~20% will have antibodies to myelin oligodendrocyte glycoprotein (MOG) IgG related disease.58 NMOSD presents with any combination of optic neuritis, transverse myelitis and area postrema syndrome (intractable nausea, vomiting or hiccups) and is typically a monophasic or relapsing illness, without progression between relapses.59