Charlie Barker’s Theory of Copper for Plants Versus Copper for Humans
Copper is present in the layperson categorization of all things: animal, vegetable, and mineral. Copper plays a vital role in different physiological functions in both humans and plants. A disequilibrium with the natural order results when copper is given to animals in the form that plants have evolved to process. Bioavailability
of copper for plants versus bioavailability of copper for humans are not the same. The general public has difficulty understanding that copper is not only toxic but essential. For some reason, mankind has been led to believe the plant copper (copper in its mineral form) is okay for humans to ingest. The proteins that chaperone copper on its way to becoming a cofactor in essential enzymes are just as highly evolved as the enzymes themselves. Animals have not evolved to utilize copper in its mineral forms as plants have. Copper in its mineral form may be toxic to animals that do not have the protein chaperones and other mechanisms to handle it. Copper in minerals Copper is one of the most unique elements on earth as it is the only mineral element that carries a plus one and a plus two oxidative state. The reader is invited to look this up. There’s no other mineral that has a plus 1/2 oxidative state, except mercury. I believe mercury is just as misunderstood as copper. This is one of the reasons that we are having major organelle toxicity with mercury because it makes the oxidation states of copper, and copper is needed in many organelle.
Inorganic, or mineral, copper is found in nature as a soft metal and in various oxide forms complexed with other elements, such as sulfur and oxygen. First of all, let me explain what is supposed to happen. Copper comes in three oxidative states. Metallic copper zero (Cu0) has zero activity. I like to call this earth copper. It has 29 protons and 29 electrons. Earth Copper becomes bioavailable to plants by the loss of two electrons to become what is known as cupric copper, or Cu 2+ (See Figure 1). Cu0 has the electronic Figure 1 Elemental copper. A. Electronic structure of uncharged copper or Cu0. Shells 1, 2, and 3 contain 2, six, and 18 electrons, respectively. There is one lone electron in the 4s subshell. Electrons from the 3d subshell have the ability to migrate up into the 4p subshell to form hybrid orbitals. B. Loss of two electrons attracts the oxygens of H2O to the Cu2+ ion. Oxygens in H2O carry a net negative charge.
structure 1s22s2p233s23p63d104s1. Or in short hand with the argon shell,
Cu0 = [Ar] 4s1 3d10
Cu+1 = [Ar] 3d10 and Cu2+ = [Ar] 3d9.
Some of these 3d electrons can be transferred to 4s and 4p shells to hybrid bonding orbitals (Figure 1B). Ligands, especially water, can form non-covalent (electron sharing) bonds. Copper in its cupric state, Cu2+, can usually be found bound to water ligands as a coordination complex (figure 1B). This micronutrient state is used by plants in soil. Soil pH is one factor that determines whether copper exists as a crystalline complex with other inorganic minerals or as a free Cu2+ cation. Figure 2 illustrates the relationship between soil pH and mineral solubility, including that of
copper. Different minerals require different reduction potentials and pH to give up their copper. If plants and/or associated microorganisms chelate copper as it is dissolved, more will be dissolved before it goes back to a mineral state.
For over 100 years, modern agricultural practices have been depleting our soils of copper, and no one is paying attention to the replacement of mineral copper for plants. As a result, all of our plants are copper-deficient before we even consume them. Fan et al. (2008) examined the mineral content of archived British wheat samples from the Broadbalk Wheat Experiment (established in 1843 at Rothamsted, UK). The concentrations of zinc, iron, copper, and magnesium remained stable between 1845 and the mid–1960s. The introduction of semi-dwarf, high yielding cultivars resulted in a decrease in the concentration of these minerals.
Copper uptake in plants
I believe water transport pathways are another route of entry because Cu2+ is surrounded by water ligands (see Figure 1). Once the Cu2+ is in the plant, it is reduced to Cu+ and chelated. I believe that this is the point in which the
Cu2+ copper becomes Cu+ copper for humans. Figure 3 Cu handling in the root symbiot Rhizophagus irregularis. The plant may acquire copper via symbiotic microorganisms. The genome of the arbuscular symbiotic root fungus Rhizophagus irregularis has been shown to contain three members of the Ctr family of Cu+ channels, as well as four genes encoding Cu+-ATPases judging from sequence similarities (Tamayo 2014). See Figure 3 for an adaptation of a schematic published in this work. Transcripts for all these transporters have been detected in symbiotic roots and germinated spores. Putative Cu transporters (Ctr) are dark orange. P1B -or Cu-ATPase (CCC2) is orange. The endoplasmic reticulum (ER) and trans-Golgi network (TGN) escort these copper proteins to the membranes. Non-copper mineral handling proteins have been removed from the original figure in Tamayo 2014 so as to focus on copper.
Other than microbial symbionts, plants use two recognized strategies for absorbing copper from soil-bound minerals. Strategy 1 is used by dicots and non-grass monocots. Strategy 2 is used by grasses.
Strategy 1 starts by acidifying the soil around the root. The rhizosphere is acidified by a mechanism similar to acidification of the mammalian stomach. This protein-mediated proton pumping into surrounding soil is regulated (Fuglsang 2014, Figure 4A). Mineral complexed copper is liberated as the Cu2+ cation. The Cu2+ cation is reduced to Cu+ by a root surface reductase, Fro4/5. The Cu+ ion is transported by a protein ion channel, COPT1 (Jain 2014, Figure 4B).
Strategy 2 absorption of mineralized copper (and iron) is initiated by secretion of chelators called phytosiderophores into the rhizosphere. (Graham RD, Stangoulis JC.2003, Figure 5A) These affinity molecules can chelate copper in equilibrium with mineral crystals. The affinity of NA for copper is 1018.6 M-1 (Curie, 2009). Just small amounts of this compound can chelate all available copper. Metal ion bound phytosiderophores (e.g. nicotianamine) are absorbed into the plant via specific transport proteins. The yellow stripe protein is one example. These transporters ferry chelated metal nutrients throughout the plant tissue (Curie 2009, Figure 5C).
Copper uptake in animals
Unlike plants, there is scant documentation for a membrane bound Cu2+ reductase like Fro4/5 in humans (van den Berg GJ, McArdle, 1994). I believe that the assumption that animals also have a Cu2+ reductase is one of the biggest misconceptions held by science and medicine regarding copper handling. Like Copt1 in plants, animals have a Cu+ ion channel called Ctr1. Therefore, I believe that Cu2+ cannot go to where it is supposed to because it is in the wrong oxidation state and on the wrong side of the membrane.
The divalent metal ion transporter, DMT1
Animals have the ability to transport Cu2+ via a divalent cation transporter, DMT1 (Figure 6A). In the dietary supplement industry, the thought is that Cu2+ supplements will interfere with Zn2+ absorption. Ironically, Arredondo et al. (2003) demonstrated that DMT1 transported Cu+ ten times better than Cu2+. The DMT1 route of entry could be considered deleterious, should it be used at all. The essential metal zinc also uses this transporter. In accordance to popular thought on Cu/Zn balance, the absorption of one could, in theory, compete with another.
Anion transporters, such as the Band 3 chloride/ bicarbonate exchanger are another possible route of copper uptake provided that the copper is complexed to chloride (Zimnicka 2011), figure 6 B,D. Note that reduction of Cu2+ to Cu+ is required prior to transport.
Another potential pathway of copper absorption in animals is in complexation with peptides found in digests of plant and animal proteins. These are numerous as copper is an essential cofactor in many plant and animal proteins called enzymes. Cu(II) complexed to triglycinate was found to pass from the mucosal to the serosal side of Ussing chamber mounted porcine small intestine (Tastet 2010), presumably via the di- and tri-peptide transporter PepT1, Figure 6C. If PepT1 transporters can be exploited for pharmaceutical uptake, surely they can transport complexed copper. Fowley et al. (2010) have reviewed the promiscuity of PepT1 as a port of entry of rationally designed drugs. Thwaites and Anderson (2007) published a thorough review of many promiscuous intestinal transporters that can be exploited for drug delivery. Hypothetically, copper could bind to natural dietary substrates of these enzymes and be transported as bound complexes.
Copper in enzymes and toxicity
Not only is copper an essential cofactor in numerous enzymes, it is also a toxin. This dichotomy arises from its redox status, flipping between Cu2+ and Cu+. Where the electron ends up determines whether it promotes or hinders health. Cytochrome c-oxidase is a copper-containing enzyme in the mitochondria. The mitochondria transfer electrons from carbon sources in the food we eat to molecular oxygen to produce water (Figure 7). Fermentation of glucose to ethanol yields two ATP (energy currency units) per molecule. The evolution of the electron transport enables the
yield of 34 ATP per glucose molecule. The dichotomous redox status of Cu allows it to accept electrons from cytochrome C and transfer them to oxygen to form water (Figure 7). This process is highly controlled. If it is not, one electron from Cu+ could just as easily be transferred to oxygen to product the reactive oxygen species superoxide.
Copper is a cofactor in the antioxidant enzyme superoxide dismutase (SOD) as well as tyrosinase, an enzyme involved in the synthesis of melanin (see figure 8). Note that copper in both of these enzymes can exist in the +1 and +2 oxidation states, like cytochrome C oxidase. Binding to oxygen is very much part of the catalytic process.
Copper-containing enzymes metabolize excess catecholamine neurotransmitters and promote collagen cross-linking. These are a few of the example of how copper molecules are used within the human body for proper physiological function. It is always a delicate balance of transferring electrons from where they need to be and not to molecular oxygen to produce the reactive oxygen species superoxide.
More of Charlie Barker’s opinions and beliefs
I revisit human copper, defined as any copper derived from plant or animal sources and plant copper as copper from inorganic complexes in the soil.
- It is my opinion that the majority of those living in North America are all copper deficient (starving for proper human copper) and at the same time, we are all copper toxic (accumulating plant copper). The subject of human copper deficiency was reviewed by Klevay (1998) prior to the USDA recommending a daily allowance; since then, Collins and Klevay (2011) have also reviewed the subject. If mineral copper is depleted from the soil, plants and the animals that eat them will in turn be copper deficient.
- I believe the modern farming techniques thought to contribute to copper decreases in cereal grains (Fan, 2008) cause copper deficiency across the board.
- I believe copper deficiency in animals is exponentially compounded when the animal is supplemented with copper in its mineral/plant form.
- I believe plant/mineral copper accumulates in our brains. While there is conjecture in the scientific community, copper in the Cu2+ form may be more prone to accumulate in deleterious deposits, such as amyloid plaques in the brains of Alzheimer’s patients, I believe we make Alzheimer’s disease and other conditions much worse by giving plant copper (Cu2+) to humans. As recently as 2015, George Brewer published numerous research and hypothesis papers linking dietary inorganic Cu2+ to the progression of Alzheimer’s disease. Environmental sources of Cu2+ are given as (1) Cu2+ dietary supplements, (2) tap water from copper-containing pipes, and (3) CuSO4 residues on produce.
Copper in brain amyloid protein aggregates. The putative structure of the extracellular copper deposits in the brain were addressed by Gunderson et al. (2012) are shown. Figure 9
Cu2+ is found at high concentrations of up to 400 μM in amyloid plaques. Cu2+
coordinates the Aβ peptides to form these organized protein aggregates. These authors showed that high molecular weight oligomers of Aβ1-40 peptides exclusively bound Cu2+ and did not redox cycle (Gunderson, 2012). This is a paradigm shift from “copper is toxic because it “redox cycles” to Cu2+ is toxic because it can “act as a “glue” in the formation of amyloid deposits.
- I believe that the liver is another site of extracellular copper deposition.
Sparks et al. (2007) addressed the interplay between liver detoxification of blood of Aβ peptides and extracellular Aβ amyloid structures in the brain. The addition of only 0.12 PPM copper (one-tenth the Environmental Protection
Agency human consumption limits) to distilled drinking water was sufficient to precipitate the accumulation of Aß in the brains of cholesterol-fed rabbits (Sparks, 2007). In a setting of elevated cholesterol, overproduced Aβ is cleared
by the blood and transferred to the liver. Aβ detoxification by the liver only occurs if copper is absent from the animals’ drinking water (Sparks 2007). If trace levels of “plant” copper (0.12 PPM) are added to the drinking water, Aβ accumulates in the brain, while the levels in the liver are greatly reduced (Sparks, 2007).
Bedlington terriers carrying mutations in the COMMD1 gene experience chronic copper-overloaded liver disease (Sarkar and Roberts, 2011). The role of the Cu2+ specific binding protein COMMD1 protein in copper export has
been reviewed by Sankar and Roberts (2011); see Figure 10 for an overview. One may speculate that if the amount of copper accumulates beyond the ability of COMMD1 and associated proteins to handle it, copper will accumulate in
the liver of humans just as it does in the livers of Bedlington terriers with COMMD1 mutations. As long as COMMD1
is functional and not pushed past capacity, all excess “plant copper” Cu2+ should be excreted conjugated to bile salts.
- If these conjugates make it to the colon, the Cu2+ has the potential to impact the colonic microflora. I believe that this is a pathway that leads to a pandemic bacterial imbalances
The Gut-Brain Axis was the topic of interest at Autism One (2016) and in the general recent peer reviewed literature. The NIH considers this interaction important and has released a Funding Opportunity Announcement to solicit proposals from small businesses and academic research laboratories to better understand this interaction.
because mineral/plant copper accumulates in humans, the copper in all dietary
supplements, processed food, and drinking water will accumulate in our extracellular matrix, favoring the brain and liver first. It is my opinion that the copper must only be consumed in the cuprous form when taking copper
supplements. There are many therapeutic benefits of proper copper amounts in dietary mineral supplementation that can be made available to humans, livestock, and performance animals. My team and I are doing the research to validate everything that I have said here. I will go public when my statements have been
proven. I will need everyone’s help in joining the cause to educate and correct this misconception and end copper toxicity and copper deficiency at the same time.
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