Preface products. These protocols have been modified from

Preface

Genetically modified food crops
developed by recombinant DNA technology aims at improving food quantity and
quality. Transgenic proteins expressed by GM crops improve crop characteristics
like nutritional value, taste, texture and endow the host plant with resistance
against fungus, pests and insects.  With
the advancements in the field of agricultural biotechnology, the number of GM
varieties ready for commercialization is increasing in proportion with the area
under GM crop cultivation and the number of countries consuming GM crops.
However, prior to release of a GM crop in the market it must pass through a
rigorous safety evaluation tests to ensure its safety for feed, fodder and the
environment. In past few decades several international regulatory authorities’
have defined guidelines for the safety assessment of transgenic food products.
These protocols have been modified from time to time and efforts are underway
to ensure complete safety of the consumers. FAO/WHO, 2001 and Codex, 2003
guidelines for safety assessment of genetically modified foods are the most
widely accepted amongst all of the available guidelines. Safety evaluation
studies do not rely on a single parameter, therefore, we take into account
results from different test to define the safety of a GM crop on a relative
scale.

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Keywords:
food
allergens, transgenic proteins,
safety testing, serum screening and genetically modified (GM) food crops

 

 

 

 

 

 

Introduction

Recent
advances in the field of r-DNA technology and improved agricultural equipments
have paved the way for large scale cultivation of genetically modified crops. Molecular biology methods are very
precise and aim at introducing only one or, at most, a few
well defined genes; rather than inserting parts of chromosomes as in
traditional plant breeding. To date, over 30 million hectares of transgenic
crops are being grown for human consumption. These are high yielding varieties resistant to pathogen attack and
tolerant to environmental imbalances like drought, cold and salinity (Huang et
al., 2005; Raman, 2017). Transgenes
expressed in GM crops encode for proteins foreign to the wild type varieties.
These proteins must be evaluated for their potency to act as novel allergens,
before using GM crops as feed or fodder. Transgenic proteins expressed in host
plant may share homology with the host plant proteins or these may share
identity with the reported food allergens (Eizaguirre et al., 2006; Romeis et
al., 2006). Therefore, prior to the release of GM crops in
the consumer market it is essential to conduct safety assessment of the GM
crops and/or transgenic proteins (Singh et al., 2008; Lu et al., 2018; Andrew
et al., 2018). Along with this GM food labeling should also be made mandatory
for all new and existing varieties.

Food
allergy is defined as an adverse health effect arising from a hypersensitivity reaction induced upon
exposure to a particular food allergen that occurs reproducibly on subsequent
exposures. Type 1 hypersensitivity food allergic reactions are
characterized by activation of mast cells and basophils, and
results in histamine release followed by synthesis of other inflammatory
molecules like leukotrienes, prostaglandins, cytokines etc.  These events manifest into severe allergic
symptoms like eczema,
hives, allergic rhinitis, asthma and gastrointestinal (GI) tract allergies. Food
allergy is reported by individuals of all age groups; however, the current
prevalence reported is 10% of children and 6% of the adults in Western countries (Sicherer &
Sampson, 2018). In general population – self reported prevalence of food
allergy ranges from 5% in Korea, 3.5% in France and 22.2% in Australia (Falcáo
et al., 2004). Food allergy is a major
health issue, and food related allergic reactions can often be life threatening
like food induced anaphylaxsis (Allen and Koplin, 2012). Food allergic
reactions may be IgE-mediated, non–IgE-mediated, both IgE/non-IgE mediated, or
cell-mediated immune reactions, induced upon exposure to the allergenic food.

In Europe and
most of the Western countries, 90% of the food allergic reactions are elicited
due to exposure to one or more of the following commodities like – milk, egg,
wheat, soy, peanut, tree nut, shellfish and fish (Sampson, 1999). However, the
prevalence of food allergy is greatly influenced by age and dietary
habits. 

 

Regulatory guidelines for safety assessment
of transgenic proteins 

Protocols
commonly used for safety assessment of GM food crops are drafted in compliance
with internationally acclaimed guidelines released by Organization for Economic
Cooperation and Development (OECD) (OECD, 1993), Food and Agriculture
Organization (FAO) of the United Nations/World Health Organization (WHO)
(FAO/WHO, 2001) and the Codex Alimentarius Commission (Codex, 2003).

For
the first time, when the need to evaluate the safety of the GM crop was felt,
it was compared to its native counterparts. The aim was to identify differences
between the two types of varieties (GM/non-GM) and whether the differences
would account for any unintended allergies. Later, FAO & WHO in 1991, in a
joint consultation proposed the idea of substantial equivalence (SE), and later
in 1993 OECD further elaborated on the principles of “SE” (OECD, 1993). Joint
FAO/WHO Expert Consultation on ‘Safety Aspects of Genetically Modified Foods of
Plant Origin’ proposed the usefulness of the concept of substantial equivalence
and concluded that “there were presently no alternative strategies that
would provide a better assurance of safety of GM foods than the appropriate use
of the concept of substantial equivalence”. Substantial equivalence (SE)
measures whether the genetically modified variety is safe as its traditional
counterpart, if such counterpart exists or to an earlier approved variety. SE
is evaluated on a scale of three – where one (1) refers to
“complete”, two (2) means “partial” and three (3) stands
for “not at all”. SE (1) implies that the GM food is similar to the
native counterpart; SE (2) explains that GM food is substantially equivalent
except for the inserted gene and SE (3) i.e. ‘not at all’ means that the GM
food is not at all equivalent to its counterpart and thorough evaluation of the
transgenic food is mandatory (Kupier et al., 2002). However, the comparison of
the GM & non-GM varieties is bound by certain limitations; like both the
varieties should be grown under similar environmental conditions and the choice
of the statistical designs for field trials should be similar for both the
varieties. A detailed safety assessment strategy involves step by step
evaluation of the transgenes expressed in the host plant (Metcalfe et al.,
1996; Panda et al., 2013).

Most commonly used safety assessment protocols primarily
evaluate the source of the transgenes, followed by bioinformatic studies to
compare the transgenic protein sequences with the reported allergens. Depending
on the results obtained for the preliminary tests, the transgenic protein is
assessed for pepsin resistance (simulated gastric fluid digestion), thermal
stability, and IgE binding with food allergic patients’ sera (serum screening
by ELISA) (Mishra et al., 2010; Arora and Mishra, 2011).

            As per the decision tree proposed
by FAO/WHO, 2001 (Figure 1), weight of evidence approach by Codex, 2003
(FAO/WHO, 2001), and guidelines given
by ICMR, 2008 (ICMR, 2008) below are mentioned some of the parameters to be
assessed for safety testing of GM crops:

 

Source
of the gene: Use of recombinant DNA
technology for development of genetically modified food crops involves transfer
of genes from a wide variety of organisms (donors). However, the conventional
breeding programs involved crossing between closely related species or genera.
Therefore, regulatory bodies have laid emphasis on evaluating the source of the
transgene, because diversity in selection of the donor species may account for
unforeseen allergenicity. Nordlee and group in 1996, reported
that transgenic soybeans expressing 2S albumin
(major allergen) protein from Brazil nut, displayed allergenic properties. And
this was one of the landmark studies, emphasizing on the importance of
evaluating the source of the transgene for developing GM food crops. Depending
on the information available transgene donors have been categorized as
allergic/non-allergic or moderately allergic. Events where the GM food crops,
contains genes from sources with known allergenic properties, rigorous in vitro
and in vivo safety testing procedures are employed to ensure safety of the GM
product  (Nordlee et al., 1996).