Primary pathology of goniodysgenesis –detected by gonioscopy- as well

Primary congenital glaucoma (PCG) refers to the disease condition
that results from the elevation of the intraocular pressure due to obstruction
of aqueous outflow by an isolated maldevelopment of the aqueous outflow
pathways (Stamper RL,
Lieberman MF, Drake MV. Developmental and childhood
glaucoma. In: Stamper RL, Lieberman MF, Drake MV, eds. Becker-Shaffer’s
Diagnosis and Therapy of the Glaucomas, 8th ed. Amsterdam: Mosby, Elsevier;
2009:294-329.). The clinical features of the disease encompass the
causative pathology of goniodysgenesis –detected by gonioscopy- as well as the
secondary effects in the eye, including elevated intraocular pressure (IOP),
enlarged –possibly cloudy- cornea with a broad limbus, a deep anterior chamber (AC)
–readily accessible for aqueous humour (AH) sampling- and an enlarged axial length,
among others (Fernandez LM, Martinez-de-la-Casa JM, Garcia-Bella J, Mendez C,
Saenz-Frances F, Garcia M, Escribano J, Garcia-Feijoo J. Clinical Variability
of Primary Congenital Glaucoma in a Spanish Family With Cyp1b1 Gene Mutations.
(J Glaucoma 2015;24:630–634).

The eye develops in utero as an outpouching of the forebrain
that forms the primitive optic vesicle. The anterior segment of the eye is a
descriptive term for the part of the eye that includes and lies anterior to the
pars plicata of the ciliary body. This anterior segment of the eye develops
from all 3 germ layers of the embryo, namely surface ectoderm, mesoderm,
endoderm, as well as neural crest cells (Abdo,
M., Haddad, S. and Emam, M. (2017), Development of the New Zealand White Rabbit
Eye: I. Pre- and Postnatal Development of Eye Tunics. Anat. Histol. Embryol.,
46: 423–430. doi:10.1111/ahe.12284423–430. doi:10.1111/ahe.12284). The
angle of the AC and specifically the trabecular meshwork (TM) develops from
neural crest cells that invade the area of the angle of the AC around the
second gestational month (Seefelder R, Wolfrum (1906) Zur Entwicklung der
Vorderen Kammer und des Kammerwinkels beim Menschen nebts Bemerkungen uber ihre
Entstehung bei Tieren. Grafes Arch Ophthl 63:430–451). Development of the
anterior segment of the eye is under the influence of a number of genes through
their secretory proteins, including PAX6, PAX2, BMP4 and the sonic hedgehog
protein, just to name some (Lupo G, Andreazzoli M, Gestri G, Liu Y, He RQ, Barsacchi G.
Homeobox genes in the genetic control of
eye development. Int J Dev Biol. 2000;44(6):627-36.).

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The composition
of the aqueous humour (AH) includes electrolytes, organic solutes, growth factors,
cytokines, and proteins (To
CH, Kong CW, Chan CY, Shahidullah M, Do CW. The mechanism of aqueous humour
formation. Clin Exp Optom. 2002;85:335–349, Freddo TF. The Glenn A. Fry Award
Lecture 1992: aqueous humor proteins: a key for unlocking glaucoma? Optom Vis
Sci. 1993;70:263–270, McLaren JW, Ziai N, Brubaker RF. A simple
three-compartment model of anterior segment kinetics. Exp Eye Res. 1993;56:355–366),
the concentration of the later
being quite small, in the range of 120 to 500 ng/?L and although derived from
plasma proteins, are structurally and functionally different. Little is known about
the protein composition of the AH, with less than 150 proteins identified so
far by different techniques including differential protein expression and
Multidimensional Protein Identification Technology (MudPIT) (Richardson MR,
Price MO, Price FW, et al. Proteomic analysis of human aqueous humor using
multidimensional protein identification technology. Mol Vis. 2009;15:2740–2750).
One robust method currently available to analyse peptides, proteins and most
other biomolecules –up to the femtomole level– is the Matrix-assisted laser
desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) (Matrix-assisted
Laser Desorption/Ionization Mass Spectrometry in Peptide and Protein Analysis

J. Kathleen Lewis, Jing Wei, and Gary Siuzdak in Encyclopedia of
Analytical Chemistry R.A. Meyers (Ed.) pp. 5880-5894 . John Wiley & Sons
Ltd, Chichester, 2000, Int J Med Sci.
2011; 8(1): 39–47. MALDI-TOF MS Combined With Magnetic Beads for Detecting
Serum Protein Biomarkers and Establishment of Boosting Decision Tree Model for
Diagnosis of Colorectal Cancer, Chibo Liu, Chunqin Pan, Jianmin Shen, Haibao
Wang, and Liang Yong, Lin
Wang, Chuanhao Tang, Bin Xu, Lin Yang, Lili
Qu, Liangliang Li, Xiaoyan Li, Weixia Wang, Haifeng
Qin, Hongjun Gao. Mass spectrometry-based serum peptidome profiling
accurately and reliably predicts outcomes of pemetrexed plus platinum
chemotherapy in patients with advanced lung adenocarcinoma

PLOS, Published: June 8, 2017). MALDI-TOF-MS
utilizes matrix-assisted laser desorption ionization of functionalized magnetic
beads to provide high sensitivity mass analyses to separate the different
protein components of a study sample.(i,ii)
Highly consistent high-throughput is assured by automated use of these magnetic
beads.

The AH is the secretory product of the non-pigmented ciliary
epithelium of the ciliary body (Civan MM, Macknight AD.
The ins and outs of aqueous humour
secretion. Exp Eye Res. 2004 Mar;78(3):625-31.). Its
composition is a function of the ciliary body as well as of the other
structures of the anterior segment of the eye consuming and producing different
compounds according to their functions and normal metabolism (Goel M,
Picciani RG, Lee RK, Bhattacharya SK. Aqueous Humor Dynamics: A Review. The Open Ophthalmology Journal. 2010;4:52-59.
doi:10.2174/1874364101004010052.). The AH as such could be viewed
as the tissue fluid of the anterior segment of the eye. Having said so, it
would be reasonable to hypothesise that the AH composition could be an
indicator of the anterior segment development and functioning, and studying the
composition of this majestic fluid is likely to yield valuable information
about the anterior segment of the eye, and proteins are but one component of
the AH that can be studied for this aim. Hence, the aim of this study was to
study the proteomic profile of AH in a number of PCG children using  MALDI-TOF MS and SPE and compare this
to a control group of as nearest as possible –at least hypothetically- to the
normal AH composition.

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