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Abstract

Objective:

To determine the frequency with which suspected pathogenic factors, including metals and metabolites that might contribute to Alzheimer's disease (AD), may be found in patients with cognitive impairment through commonly available blood tests.

Methods:

A variety of serum studies, including metals, ammonia, homocysteine, vitamin B12, folate, thyroid tests, metabolic products, and inflammatory markers, were measured in two cohorts: one meeting mild cognitive impairment (MCI) criteria and the other meeting mild-to-moderate dementia (DE) criteria. Medications these patients received were reviewed.

Results:

Metal abnormalities were detected in over half the subjects, including evidence of mercury, lead, and arsenic elevation as well as instances of excessive essential metals, iron (Fe), and copper. Some metal aberration was detected in 64% of the DE group and 66% of the MCI group. Females were more likely to have elevated copper, consistent with hormonal effects on copper excretion. Homocysteinemia was the most common abnormality, detected in 71% with DE and 67% with MCI, while methylmalonic acid was not elevated. Slight hyperammonemia was moderately common (38%) suggesting a hepatic factor in this subset. Findings of moderate insulin resistance were present in nearly half (44% DE, 52% MCI). Sixty of 65 (92%) had at least one abnormal biomarker and 60% had two or more. The most common drug taken by the total cohort was proton pump inhibitors at 22% DE and 38% MCI.

Conclusions:

This study suggests that both toxic metals and excessive vital metals such as copper and iron, as well as common metabolic and hepatic factors are detectable at both stages of MCI and DE. There appears to be a multiplicity of provocative factors leading to DE. Individualized interventions based on these parameters may be a means to reduce cognitive decline leading to DE. A more comprehensive prospective study of these environmental and metabolic factors with corrective early interventions appears warranted.

Introduction

As research has progressed, plasma biomarkers for Alzheimer's disease (AD) are emerging. Among leading biomarkers at present is P-tau 181, which correlates with longitudinal cognitive decline and temporal lobe gray matter loss.¹ While this marker correlates well with neuronal destruction, it does not suggest a pathogenic factor that can be reversed or treated. Similarly, plasma neurofilament light chain (NfL) is a general biomarker of neurodegeneration² and affords no insight into pathogenic factors. While these and other biomarkers may aid in the diagnosis of a particular patient with cognitive impairment, they measure a molecular endpoint rather than a pathogenic factor.

In searching for potential pathophysiological markers that can be readily assessed and are suggestive of a therapeutic approach, the authors conducted an exploratory study in a clinical setting of two groups of patients with disturbed cognition, one with mild-to-moderate dementia (DE) and another with mild cognitive impairment (MCI). Among the diverse potentially pathogenic factors the authors measured were selected metals, homocysteine, ammonia, a surrogate for insulin resistance (glycosylated hemoglobin; HbA1c), markers of systemic inflammation, and vitamin folate and B12 levels.

Homocysteine is a leading metabolic factor in the development of AD: the odds ratio of cognitive decline is 2.8-fold higher for homocysteine levels above 15 μmol/L than those below 10 μmol/L.³ Moreover, in another study, 85% of patients experiencing a stroke had a homocysteine greater than 10.⁴ Not surprisingly, homocysteine above 10 μmol/L contributes to both vascular dementia (VD) and AD,⁵ the two leading causes of DE. A meta-analysis suggested considerable heterogeneity exists in prior studies.⁶

Ammonia is the most common endogenous neurotoxin and may accumulate in the brain to toxic levels. Hepatic encephalopathy is closely linked to ammonia toxicity and resembles AD in some respects.^7,8 Furthermore, those with AD have been found to demonstrate elevated brain ammonia, and in some studies, modest elevation of serum ammonia concentrations.⁹

Elevated ammonia appears to be neurotoxic because it can disrupt glucose metabolism, promote mitochondrial dysfunction, impair glutamatergic and GABAergic neurotransmission, harm NMDA receptors, and activate the inflammatory response.⁷ Also underlying the importance of hepatic dysfunction in AD is the study finding an elevated aspartate aminotransferase (AST) to alanine aminotransferase (ALT) with odds ratio 7.92 as well as other serum markers of liver function.¹⁰

Metal toxicity appears to be a key component regarding the development of AD, and it is not a single metal that is a concern but several diverse ones.¹¹ Even essential metals such as iron (Fe), selenium (Se), copper (Cu), and zinc (Zn) may be toxic if present in excess. A nuanced review of this topic notes that while organic selenium is essential for adequacy of selenoproteins vital for brain health inorganic selenium such as selenite is likely toxic.¹²

Similarly copper and zinc may be protective or toxic depending on their valence and bound state as well as the quantity present. Iron may have a particular role as well since the type of cell death ferroptosis may be increased with iron excess particularly when there is glutathione depletion and lipid peroxidation present.¹³

Metallic nanoparticles and metallic oxide nanoparticles are particularly likely to cross the blood–brain barrier (BBB) inflict oxidative stress, and evoke inflammatory responses from microglial cells, particularly in the hippocampus and the cerebral cortex.¹¹ Oligo elements of this type can also cause oxidative and inflammatory injury. These toxicants can enter the body through ingestion, inhalation, and occasionally percutaneously.

Neurodegenerative disorders such as AD may then proceed from a combination of inflammatory factor release, generation of reactive oxygen species, apoptosis, ferroptosis, and autophagy within glial cells and accompanying neurons. This exploratory study assessed the frequency of such biomarkers in two populations of patients with measurably impaired cognitive function, possibly suggesting new directions for future research.

Methods and Materials

A convenience sample of 69 primary English-speaking participants (35 females and 30 males) was identified from the population of patients previously evaluated clinically for cognitive decline at the cognitive neurology clinic at Thomas Jefferson University Hospital in Philadelphia, Pennsylvania. The sample was divided into two groups: those with MCI (n = 29) and those with DE (n = 36).

The group had a mean age of 72.9 (standard deviation [SD] = 8.5 years). In terms of race and ethnicity, 1.5% of the sample was Asian, 16.9% were Black, 1.5% were Hispanic, 75.4% were White, and 4.6% were of another or unspecified racial or ethnic group. None had early-onset DE.

See Table 1 for demographic variables and mean Montreal Cognitive Assessment (MoCA) scores.

Table 1.

Demographics and Montreal Cognitive Assessment Scores in Two Cohorts

	Mean age	% Female	Education (% in each group)				Mean education	Converted MoCA score ^a
	Mean age	% Female	≤HS	HS diploma	Some college to college degree	Post-college	Mean education	Converted MoCA score ^a
MCI	70.9 (8.5)	48.3	6.9	17.2	41.4	34.5	15.8 (2.8)	24.4 (2.1)
Dementia	74.5 (8.3)	58.3	14.3	31.4	42.9	11.4	14.4 (2.5)	13.5 (6.5)
Total sample	72.9 (8.5)	53.8	10.9	25.0	42.2	21.9	15.1 (2.7)	18.4 (7.4)

Significant difference between groups at <0.001 level.

HS, High School; MCI, mild cognitive impairment; MoCA, Montreal Cognitive Assessment.

A subset of these participants also completed standard of care neuropsychological (NP) assessment documenting the presence of MCI or DE. MCI was defined by subjective cognitive decline and objective cognitive dysfunction based on the presence of multiple scores on standardized tests below the age and education corrected normative samples that represented a decline from their estimated baseline, without significant functional decline.¹⁴

However, because the NP assessment was completed as standard of care clinically, exact quantitative¹⁴ criteria (i.e., scores exactly at or under −1.5 SDs below the age and education corrected mean) were not always used. For example, an individual may have had subjective cognitive decline and several scores below their estimated premorbid level of functioning that were thought to represent decline based on the neuropsychologist's clinical impression.

DE diagnosis would require the appropriate cognitive test score criteria, with the additional documentation of functional decline in activities of daily living,¹⁵ such as driving, financial or medical management, food preparation, or community participation. For those participants who did not have full NP assessment, the cognitive neurologist's evaluation and diagnosis was used for documenting MCI or DE.

This evaluation typically consisted of a comprehensive history with collateral report when available, neurologic examination, and completion of mental status examination (i.e., either the Folstein Mini Mental Status Examination [MMSE]¹⁶ or the MoCA,¹⁷ or both). Likely etiology of DE (e.g., Alzheimer's, vascular, Lewy body DE, mixed or the pattern of MCI; e.g., amnestic, non-amnestic, and single or multidomain) was classified by a cognitive neurologist, clinical neuropsychologist, or both.

Individuals with significant psychiatric, medical (e.g., chronic kidney disease and hepatic encephalopathy), or other neurologic disorders that could account entirely for cognitive impairment were excluded. See Table 2 for key medical history variables. Initial or follow-up visit blood work ordered to rule out reversible causes of cognitive impairment was used to assess the presence of abnormal serum biomarkers. Because the tests were ordered clinically and completed at the patients' discretion, confirmation that they were fasting could not be confirmed.

Table 2.

Medical Disorders in Dementia and Mild Cognitive Impairment

% Sample with	Diabetes diagnosis	GERD	Heart disease	Hyperlipidemia	HTN	Hypothyroidism	Sleep apnea	Stroke
Dementia	11.1	16.7	36.1	55.6	55.6	25.0	5.6	11.1
MCI	27.6	34.5	34.5	41.4	51.7	10.3	20.7	3.4

GERD, gastro-esophageal reflux disease; HTN, hypertension; MCI, mild cognitive impairment.

The authors used a homocysteine level of 11 μg/dL as elevated as indicated in a consensus statement,¹⁸ although 10 μg/dL and above is associated with cognitive impairment.⁵ They used a copper level of 140 μg/dL¹⁹ as the cutoff, and 8 μg/dL for arsenic.²⁰ Vitamin B12 below 300 μg/dL required further investigation.²¹ They used HbA1c as a proxy for insulin resistance, it having been shown that a slight elevation of HbA1c was associated with significant insulin resistance.²² See Table 2 for medical disorders that the patients had diagnosed.

Right-handed individuals made up 90.6% of the sample, while 9.4% were left-handed. There were no statistically significant differences in age or education between groups. Jefferson University Institutional Review Board (IRB) approval was granted for retrospective chart review and data analyses.

Statistical analyses

Evaluating the difference in mental status examination performance between groups was completed by first converting MMSE scores to MoCA scores for a common metric, as the sample sizes for each MMSE and MoCA were too small to analyze separately. As the MoCA has been shown to be more sensitive to milder degrees of cognitive impairment and conversions have been previously validated,^23,24 the authors chose to convert MMSE to MoCA scores using the conversion factor from Roalf et al.²⁵

The difference between MoCA scores between groups was calculated using the Mann–Whitney U test due to the non-normal distribution of MoCA scores. No subgroup analyses based on likely etiology of DE (e.g., Alzheimer's and vascular) were used due to the small sample size. The primary analyses to determine if there were differences in the frequencies of key medical diagnoses and elevated biomarkers between MCI and DE groups were completed using chi square or Fisher's exact test when chi square cell counts were below five.

Binary logistic regression was completed to determine if biomarker elevations predicted group membership (MCI vs. DE); all biomarkers were entered in a single step. Outlier variables were winsorized by reducing their value to the next highest value.²⁶ Odds ratios were calculated to determine if elevations in copper were associated with elevated risk of other metal elevations (i.e., arsenic, ferritin, lead, and mercury). All statistical analyses were completed in IBM SPSS statistics for Windows, version 26 (IBM Armonk, NY, 2019). A STROBE guideline checklist was utilized.

Results

The key biomarker findings are summarized in Table 3. In Table 4 are the actual values obtained for the DE group. All but 5 of 65 (92%) participants had at least 1 abnormal biomarker, and 60% had 2 or more.

Table 3.

Serum Metabolic and Metal Parameters Levels

% Samples ^a with elevation of	MCI	Dementia
Homocysteine (>11 μmol/L)	67 (n = 24)	71 (n = 31)
Arsenic (≥8 μg/dL)	20 (n = 25)	12 (n = 34)
Lead (≥3 μg/dL)	16 (n = 19)	16 (n = 31)
Mercury (≥5 μg/L)	26 (n = 23)	12 (n = 26)
Copper (≥140 μg/dL)	8 (n = 24)	15 (n = 31)
Copper (≥132 μg/dL)	8 (n = 24)	29 (n = 34)^**
Ferritin (>300 ng/mL)	16 (n = 25)	15 (n = 32)
One or more elevation: all metals^a	66 (n = 29)	65 (n = 36)
Hemoglobin A1c (>5.6%)	52 (n = 23)	44 (n = 25)
Ammonia (>35 μmol/L)	40 (n = 28)	36 (n = 33)
B12 (<300 pg/mL)	12 (n = 25)	9 (n = 30)

Percentage of total samples tested for that compound or element.

p < 0.05.

MCI, mild cognitive impairment.

Table 4.

Metabolic Values in Dementia Cohort

Homocysteine	HbA1C	Ammonia	Vitamin B12	TSH
>11 μmol/L	>5.6%	>35 μmol/L	<300 pg/mL	>5 mIU/L or <0.4
13.2	5.4	43	381	1.89
17.3		38	440
12.0	5.9	34		2.26
11.6	5.8	49	968	0.33
11.8	5.0	19	594	1.60
14.8	5.2	24	535	0.89
18.7		43	719
8.3	5.6	38	807
30.0		32	212	1.37
10.0		36	554	0.84
17.4	6.0	34	313	2.75
12.4	5.7	33	1820
11.8			833	2.11
15.3	5.3	21	500	7.61
11.2	6.0	30	1697	1.71
17.9	5.6	27	515	3.78
10.0	6.3	24	474	1.16
15.5	5.2	23	436	0.91
17.0	5.3	58	466	1.45
15.4	5.4	13	450	2.44
8.6		40	782	2.21
13.6	6.4	42	517	1.45
9.8	5.2	30	368	2.17
9.7	5.8	16	246	2.22
6.5	5.7	20	1125	2.27
11.6	5.6	49	408	0.01
10.0	5.9	35	414	1.68
14.9	9.3	18	732	3.18
18.2	5.7		365	3.38
15.6	5.4	15	777	17.24
9.4	5.9	16	250	1.29
		38	619	2.10
		36	433	1.58
		59	304	3.41
		22		0.81
22/31	11/25	12/33	3/32	3/31
71%	44%	36%	9%	9%

Some metal abnormalities were detected in almost two-thirds of the subjects (64% DE and 66% MCI), including evidence of mercury, lead, and arsenic elevations, as well as instances of excessive essential metals, iron and copper. There was a significant difference between groups in the frequency of copper elevation when the level of copper elevation included cases above 132 μg/dL [χ² (df = 1, N = 55) = 4.539, p = 0.033].

Individuals with DE were more likely to have a copper elevation above 132 μg/dL. Follow-up chi square analyses revealed that, between males and females, there were significant differences in elevations of copper using a cutoff of 132 μg/dL; [χ² (df = 1, N = 55) = 5.130, p = 0.024], with females having a higher frequency of elevated copper.

Homocysteinemia was the most common single abnormality (71% DE and 67% MCI), while methylmalonic acid (MMA) was not elevated at all. There was also a sex difference regarding homocysteine, with males having a higher frequency of elevated homocysteine [χ² (df = 1, N = 53) = 4.780, p = 0.029]. Ammonia was elevated in 40% of the MCI group and 36% of the DE group, and the two groups were not significantly different.

There were no significant differences between groups in frequencies of key medical diagnoses, including diabetes, gastroesophageal reflux, heart disease, hyperlipidemia, hypertension, hypothyroidism, sleep apnea, and stroke (Table 2). There were also no differences between groups in the frequencies of elevations of ammonia, arsenic, copper (elevated above 140 μg/dL), ferritin, homocysteine, HbA1c, lead, mercury, or low B12 level (Table 3).

Medications

The authors also examined whether participants were on classes of medications known to be associated with cognitive impairment, including proton pump inhibitors (PPIs),²⁷ the anticonvulsant valproic acid,^28,29 and a subset of anticholinergic medications.³⁰ This was accomplished by searching electronic medical records for medications listed as current or active. PPIs searched included esomeprazole, esomeprazole magnesium/naproxen, omeprazole, aspirin/omeprazole, omeprazole/sodium bicarbonate, dexlansoprazole, lansoprazole, pantoprazole, and rabeprazole. Anticholinergics included belladonna alkaloids, benztropine, clidinium-chlordiazepoxide, dicyclomine, festerodine, flavoxate, hyoscyamine, methscopolamine, oxybutynin, propantheline, scopolamine, solifenacin, tolterodine, trihexyphenidyl, and trospium.

Of the total sample, 29% (19/65) were on PPIs and 8% were on anticholinergics (5/65). No one was taking valproic acid, a known cause of hyperammonemic encephalopathy.³¹ In the MCI group 38% were on a PPI and 10% were on anticholinergics, while in the DE group 22% were on PPIs and 6% were on anticholinergics.

Discussion

The authors completed an exploratory study in two groups of older adults with cognitive impairment that examined several potentially contributing pathogenic factors in the development of DE based on current neuroscience research. They found moderately compelling evidence of metal toxicity of various metals even though the study design did not include urine, hair, or nail analysis that would have likely detected a greater extent of metal toxicity.

The metals identified included known toxic ones such as mercury, arsenic, lead, and cadmium, as well as an excess of essential metals, iron and copper, which can become toxic when present in excessive quantities. Hypercupremia was significantly more common in females, as estrogen and progesterone tends to raise both copper and ceruloplasmin, possibly by reduced bile³² or renal excretion. The authors did not measure aluminum, another metal that has been associated with the development of DE.³³

Metals can promote DE through several mechanisms

Metals increase immune responses, including delayed hypersensitivity and antibody responses to antigens as evidenced by their use as adjuvants, among other evidence.³⁴ Genetic differences determine individual susceptibility to this effect. Metals may also interfere with the hypothalamic–pituitary–adrenal axis.

Metals evade the BBB by exchanging with calcium, mechanisms normally used by copper and iron. Once past the BBB, toxic metals induce excitotoxic neuronal injury, oxidative stress, reactive oxygen species, and mitochondrial injury. There is increasing evidence linking metal toxicity to AD.^35,36

Toxic metals can also have an indirect negative effect on brain health by promoting gut dysbiosis. Toxic metals such as arsenic, cadmium, and lead are among the chemicals that exert a toxic effect on the gut microbiome predisposing toward more toxic bacterial species.³⁷ Such effects have been linked to AD. Toxic metals increase inflammation in the gut, thus contributing to gut dysbiosis.³⁸

Excess iron (Fe) has been shown to disturb microglia by activating nuclear factor kappa beta (NF-κB)-mediated cytokine activation.³⁹ The Framingham study demonstrated that about 12% of the geriatric population was in fact Fe overloaded.⁴⁰ Moreover, excess Fe can cause a form of lipid peroxidation, ferroptosis, which can result in neuronal and glial death.⁴¹ Copper inhibits regulatory mechanisms of activated BV2 microglia and possesses a mix of pro-inflammatory and anti-inflammatory properties.⁴²

Italian researchers demonstrated that the free copper pool in the plasma of AD patients is elevated compared with age-matched control subjects, and they observed a “dose response effect,” with those with higher free copper levels experiencing greater loss of cognition.⁴³ Laboratory studies similarly show chronic copper exposure activates microglia inflammation and degenerative expression.⁴⁴ Of note, APOE e4, a genetic risk factor for AD, has no copper-binding cysteines, while APOE e2, which has a protective effect, has two copper-binding cysteines.⁴⁵

Researchers have shown that late-onset AD patients are zinc (Zn) deficient compared with age-matched controls, likely because Zn is a component needed for adequate glutathione metabolism and neuronal defense.⁴⁶ A pilot double-blind study of a new Zn formulation found that in patients aging 70 and over, it protected against cognitive decline.⁴⁷ Zn therapy in the aforementioned study also significantly reduced serum free copper in AD patients, so efficacy may come from restoring normal Zn levels, or from lowering serum free copper. Improved immune functioning may be a factor as well, as adequate Zn stores are needed for proper immune functioning.

A series of inflammatory signaling molecules are upregulated by arsenic, including tumor necrosis factor-α (TNF-α); the interleukins (ILs)—IL-6, IL-8, IL-12, and NF-κB, activating inflammatory responses and oxidative stress, and blocking the protein degradation of the ubiquitin-proteasomal pathway.⁴⁸ All of these pathologic processes can contribute to the development of AD.⁴⁹ It has been described in detail that arsenic environmental poisoning correlates with cognitive impairment in China.⁵⁰

Geological information relevant to the cohort of patients includes that the U.S. Geological Survey has identified an excess concentration of arsenic in the groundwater in approximately 30% of sources in southeastern Pennsylvania, predominantly in the Newark basin. Drinking unfiltered water with elevated arsenate or arsenite could be a predisposing factor and may take decades of exposure to have an effect.⁵¹

Regarding lead (Pb) exposure, lifetime exposure is associated with accelerated reduction in cognition as well as an increased prevalence of late-onset DE.⁵² The authors found evidence of lead exposure in 16% of those assessed, but more may have tested positive if they measured nail Pb. Metal toxicity is also associated with both hearing loss⁵³ and macular degeneration⁵⁴ both of which are also risk factors for development DE.

Homocysteinemia, a well-known risk factor and putative cause of DE, was the single most frequent abnormality in this study, 71% in the DE group and 67% in the MCI group. It is important to note that in addition to folate and vitamin B12, pyridoxine is essential for keeping homocysteine at normal levels. Risk factors for pyridoxine deficiency include malabsorption, bariatric surgery, renal insufficiency with renal replacement therapy, poor diet, and the drug isoniazid.⁵⁵ Diagnosis of pyridoxine deficiency is usually clinical and may be missed if not considered. Cognitive impairment is one symptom of deficiency.

In addition, when encountering patients with elevated homocysteine, a subset may have the methylenetetrahydrofolate reductase (MTHFR) 677 TT SNP gene mutation and thereby require the methylated forms of folate and vitamin B12 to correct homocysteinemia.⁵⁶ Studies suggest the MTHFR 677T polymorphism is a risk factor for AD in Asians and those with the ApoE4 mutation but perhaps not in all Caucasians.⁵⁷

Elevation of MMA was not found, questioning its utility in ruling out functional vitamin deficiencies. Neurologists should know that they need to measure homocysteine and not rely on MMA levels.

Mild hyperammonemia was present in 36% of the DE group and 40% in the MCI group and was not sex weighted. It has been suspected to be a pathogenic factor in the development of DE for quite a while and several mechanisms have been suggested. Ammonia increases reactive oxidative species and decreases the activity of such key enzymes as glutathione peroxidase, which plays a key role in mitochondrial function and neuronal protection.⁹ Excess propionate in the gut has been linked to AD, possibly mediated by hyperammonemia.⁵⁸ It may also be a marker of impaired liver function more generally, including synthetic functions. This study suggests further evidence of the liver–brain nexus.

Insulin resistance indicated by elevated HbA1c as in the metabolic syndrome was common (44% in DE group and 52% in MCI group), while fully developed diabetes mellitus, type 2, was less common (11% in the DE cohort and 28% MCI group). Insulin resistance appears to play a crucial role in AD development.⁵⁹ Thyroid stimulating hormone abnormalities are noted but may have pathologic significance because low TSH has predictive value for the development of AD.^60,61 When found, these abnormalities need to be addressed.

Elevated erythrocyte sedimentation rate (ESR) was occasionally found and may require a rheumatologic evaluation. However more subtle markers of inflammation such as highly sensitive C-reactive protein (CRP) and IL-6 are often elevated in both DE and MCI,⁶² reflecting an inflammatory state.

Among the medications, PPIs stand out with 22% in the DE group and 38% in the MCI group taking one. Researchers in Germany,²⁷ in a pharmacoepidemiologic study of over 70,000 patients over the age of 75 years, found those taking a PPI had an odds ratio of 1.44 of developing DE compared with those who were not taking one. Research in India indicates that PPIs may be contaminated with heavy metals such as cadmium and iron.⁶³

This may be more common with generic versions. PPIs, trade brands or generic, may also interfere with vitamin B12 absorption,⁶⁴ particularly if more than one dose a day is taken. Vitamin B12 deficiency could contribute to the development of DE through homocysteinemia. It would appear judicious to further evaluate the possible contribution of PPIs to the development of DE.

Limitations

It is important to note that the authors only measured a subset of potential pathogenic biomarkers. Aluminum, manganese, and cobalt were not measured, nor did they measure metals in the urine, hair, or nails. Some metals quickly leave the bloodstream so measuring them in nails and urine in addition to serum is essential for a thorough assessment of metal toxicity. Both epidemiologic as well as experimental studies have demonstrated the importance of metals such as manganese, cadmium, and lead to the development of AD and other DEs supporting the need for such measurements.⁶⁵

The authors did not measure any direct parameter of gut dysbiosis although the elevated ammonia may be an indirect measure of it. The oral microbiome may also be a factor as there is increasing evidence that chronic gingivitis may be a contributory factor to microglial activation in AD.⁶⁶ The authors did not measure parameters of “inflammaging” such as TNF and IL-6, nor did they measure lipid peroxidation parameters such as isoprostanes or exposure to mycotoxins, which also may have a role in AD.⁶⁷

The authors did not have a control group that has normal cognitive function but that if often lacking in an exploratory study. The abnormal biochemical findings may be found in those with normal cognitive function even though there is ample research evidence that these factors may contribute to the development of AD. Whether a given potential toxin may express toxicity as cognitive impairment in a given individual may be a function of the net total load of provocative factors balanced against protective factors, including nutritional, environmental, and genetic factors.

The sample size is small but suitable for an exploratory study.

Conclusions

A great preponderance of study subjects had at least one potentially pathogenic biomarker abnormality (92%), either metabolic or environmental, and 60% had two or more abnormal markers. This is one of the first studies to examine this multitude of potential pathogenic factors in a population of patients with MCI and mild-to-moderate DE. It thus may help illuminate the frequency of these factors and suggests the design of future clinical studies of this disorder that may permit more definitive conclusions.

This exploratory study suggests that several potentially pathogenic factors are present in individuals with evidence of cognitive impairment. It should serve as a stimulus to open the black box of probable pathogenic factors in the development of DE so that effective preventive interventions are developed and implemented.

A pilot study of a similar cohort with either MCI or DE evaluated patients for a broad range of potential toxicants and formulated individualized therapy found 72% of patients had marked or moderate improvement.⁶⁸ Treatments included a ketogenic diet for insulin resistance and detoxification if metal toxins were found.

Increasingly late-onset AD is appearing less like a disease with a single pathogenesis and more like one with many pathogenic pathways instigated by a variety of toxicants, deficiencies, and degenerative changes involving multiple organ systems in the aging human body, including the liver.⁶⁹ The organ systems involved include the immune, endocrine, gastrointestinal, and hepatic systems.

The authors' findings suggest these factors are relatively common in both cohorts, whether with MCI or DE, thus raising the hope that if identified early and matched with an effective intervention, that progression of cognitive impairment may be halted, slowed, or even reversed. The authors' data suggest a variety of metals as well as homocysteine, ammonia, and insulin resistance need evaluation and subsequent management in patients presenting with cognitive impairment.

The authors are suggesting this should be initiated at the earliest stage of cognitive impairment during the aging process. The specific intervention for a particular patient needs to be individualized based on laboratory findings of potential pathogenic factors. Much research is needed to assess the efficacy of individualized interventions, but a new era of understanding the complexity of the development of AD has begun and should be pursued vigorously.

Footnotes

Authors' Contributions

Conception by A.R.E. and C.F.L. Formal analysis by A.C.L. Data management by A.C.L. Investigation by C.F.L. and A.C.L. Initial draft by A.C.L. and A.R.E. Review by C.F.L., A.C.L., and A.R.E.

Author Disclosure Statement

No competing financial interests exist.

Funding Information

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Supplementary Material

STROBE Statement

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