Clinical Biochemistry of Domestic Animals (Sixth Edition) - UMK ...

IV. Mature RBC
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Echinocyte formation in sheep RBCs after ATP-depletion
has been attributed to the degradation of membrane phosphoinositides
( Backman et al. , 1998 ). Echinocytes and other
shape abnormalities have been recognized in dogs with
RBC pyruvate kinase deficiency, which results in a
decreased ability to generate ATP ( Chandler et al. , 1975 ;
Muller-Soyano et al. , 1986 ; Schaer et al. , 1992 ).
Although the mechanism(s) is unknown, ATP is
required for maintenance of normal shape and deformability
of RBCs ( Jacob et al. , 1973 ). Because ATP concentrations
must be depleted for a number of hours to demonstrate
changes in shape and deformability in vitro , the concentration
does not directly control these properties; rather, the
processes occurring secondary to ATP depletion alter the
shapes of cells ( Feo and Mohandas, 1977 ).
ATP is required for a number of reactions involving the
RBC membrane ( Cohen and Gascard, 1992 ). It is used as
the phosphoryl donor in a wide variety of phosphorylation
reactions involving membrane proteins and for the phosphorylation
of membrane phosphoinositides. It provides the
energy needed to pump Ca 2 out of cells. Increased Ca 2
activates neutral proteases (calpains), which can degrade
membrane skeletal proteins, and phospholipase C, which
cleaves phosphoinositides. ATP is required for the transport
of aminophospholipids to the inner half of the lipid bilayer,
presumably assisting in the maintenance of the asymmetry
of membrane phospholipids. The relative importance of
each of these ATP-dependent reactions to the maintenance
of RBC shape and deformability remains to be determined
( Cohen and Gascard, 1992 ).
2 . Acanthocytes
Acanthocytes (spur cells) are RBCs with irregularly spaced,
variably sized spicules. They can form when RBC membranes
contain excess cholesterol compared to phospholipids.
If cholesterol and phospholipids are increased to a
similar degree, codocyte formation is more likely than acanthocyte
formation ( Cooper et al. , 1972 ). Alterations in RBC
membrane lipids can result from increased blood cholesterol
content ( Cooper et al. , 1980 ) or the presence of abnormal
plasma lipoprotein composition ( Ulibarrena et al. , 1994 ).
Another possible contributing factor is the defective repair
(acylation of lysophospholipids) of oxidant-damaged RBC
phospholipids reported in human patients with cirrhosis and
acanthocytosis ( Allen and Manning, 1994 ). Acanthocytes
have been recognized in animals with liver disease, possibly
because of alterations in plasma lipid composition, which
can alter RBC lipid composition ( Christopher and Lee,
1994 ; Shull et al. , 1978 ). They have also been reported in
dogs with disorders such as hemangiosarcoma and disseminated
intravascular coagulation that result in RBC fragmentation
( Weiss et al. , 1993 ).
Marked acanthocytosis is reported to occur in young goats
( Holman and Drew, 1964 ) and some young cattle ( McGillivray
et al. , 1985 ; Sato and Mizuno, 1982 ). Acanthocytosis of
young goats has been attributed to the presence of HbC
at this early stage of development ( Jain et al. , 1980 ).
Acanthocytosis in blood is associated with a heterogeneous
group of inherited neurodegenerative disorders in
humans (neuroacanthocytosis), resulting in defects of at
least four different proteins ( Stevenson and Hardie, 2001 ).
Deficient proteins appear to be important in membranes of
neural or muscular tissues in addition to RBCs.
3 . Stomatocytes
Cup-shaped RBCs that have oval or elongated areas of central
pallor when viewed in stained blood films are called
stomatocytes. They most often occur as artifacts in thick
blood film preparations. Stomatocytes form when pH is
decreased ( Gedde et al. , 1997 ) and when amphiphatic drugs
are present that distribute preferentially in the inner half
of the lipid bilayer ( Smith, 1987 ; Suwalsky et al. , 1999,
2000 ). Stomatocytes also form when RBC water content
is increased, as occurs in hereditary stomatocytosis in dogs
(Giger et al. , 1988a ; Paltrinieri et al. , 2007 ; Pinkerton et al. ,
1974 ; Slappendel et al. , 1994 ).
4 . Eccentrocytes
Eccentrocytes are RBCs in which the Hb is localized
to part of the cell, leaving an Hb-poor area visible in the
remaining part of the cell. Other terms used to refer to
eccentrocytes include hemighosts, irregularly contracted
cells, double-colored cells, and cross-bonded RBCs ( Arese
and De Flora, 1990 ; Chan et al. , 1982 ). They are formed
by the adhesion of opposing areas of the cytoplasmic face
of the RBC membrane ( Fischer, 1986 ). Denatured spectrin
is believed to be of primary importance in the cross bonding
of membranes ( Arese and De Flora, 1990 ; Fischer,
1988 ). Eccentrocytes that have become spherical with only
a small tag of cytoplasm remaining may be called pyknocytes.
Eccentrocytes have been seen in animals ingesting
or receiving oxidants ( Caldin et al. , 2005 ; Harvey, 2001;
Harvey et al. , 1986 ; Harvey and Rackear, 1985 ; Lee et al. ,
2000 ; Reagan et al. , 1994 ) and in horses with severe burns
( Norman et al. , 2005 ). Eccentrocytes have also been seen
in horses with glucose-6-phosphate dehydrogenase (G6PD)
deficiency ( Stockham et al. , 1994 ) and glutathione reductase
deficiency secondary to RBC flavin adenine dinucleotide
(FAD) deficiency ( Harvey et al. , 2003 ). Both of these
disorders decreased the ability of RBCs to protect against
endogenous oxidants.
5 . Spherocytes and Elliptocytes
Defects in ankyrin, band 3, protein 4.2, and certain defects
is α -spectrin and β -spectrin result in hereditary spherocytosis
in mice and humans ( Delaunay, 2007 ). A complete