Background

Alzheimer’s disease (AD), the main cause of dementia, affects more than 30 million people worldwide, with a rising tendency towards the number of 100 million patients estimated to suffer from the disease in the year 2050 [1,2]. Primary open angle glaucoma (POAG) is the second cause of blindness worldwide [3]. H. pylori is a common, Gram-negative bacterium found in the stomach. It has been shown to elicit an inflammatory response (gastritis) by altering stomach pH, and by secreting proteases and VacA. It has also been implicated in the development of gastroduodenal ulcer, gastric cancer, MALT-lymphoma and colorectal cancer [4-8].

Neurodegenerative disorders are believed to be linked to each other as well as to H.pylori infection in terms of epidemiology and etiology [9-13]. However, various studies investigating the issue have concluded to contradictory results [14-16]. For this reason, aim of the current prospective study is to elucidate the putative association between Alzheimer’s disease and other dementias (frontotemporal- dementia- FTD), dementia with Parkinson’s disease-PD, Lewy body dementia-LB), primary open-angle glaucoma (POAG) and H.pylori infection in all possible combinations, based on a wide range of diagnostic procedures, that would set the diagnosis of each disorder with accuracy and beyond doubt.

Methods

The study was performed in compliance with the Helsinki Declaration and after the approval of the Ethics Committee of the Aristotle University of Thessaloniki. The patients, whose informed consent was obtained prior to the initiation of the study were divided in the following groups:

  1. i.

    A group of patients with dementia (60 patients), which included patients with official diagnosis of AD (36 patients), PD (9 patients), LB (9 patients), FTD (6 patients) [17-20].

  2. ii.

    A group of patients with POAG (35 patients).

  3. iii.

    A control group of 31 subjects found negative for dementia and glaucoma. They were used for the analysis of Hp infection incidence in patients with dementia and glaucoma.

  4. iv.

    A second control group of 30 subjects recruited from an emergency ophthalmology department, used for the analysis of correlation between dementia and glaucoma.

Neuropsychological battery

All participants were checked for dementia with the application of a neuropsychological battery consisting of the Mini Mental State Examination, the Functional Rating Scale for Symptoms of Delirium, the Neuropsychiatric Inventory, the Hindi Mental State Examination and the Geriatric Depression Scale [21-28].

Ophthalmological examination

The ocular examination was based on visual acquity control (reading of an optotype from a distance of 5 meters), tonometry with a Goldmann’s applanation tonometer [29] after application of a local anesthetic (hydrochloric proxymetacaine 0.5%), and fundoscopy after the application of tropicamide solution 0.5% and of the a-adrenergic stimulator phenylefrine in a solution of 5%. The examination was concluded with a control of visual fields in a static perimetry apparatus type Octopus 900 (Haag-Streit, Switzerland). Diagnostic criteria for glaucoma were the ones provided by the Thessaloniki Eye Study [30].

Helicobacter pylori infection diagnosis

The examination for the Hp infection was based on gastroscopy and histological examination of the retrieved tissue specimens. Gastroscopy was performed after induction of sedation with midazolame (Dormicum) in an iv. administration and in a dosage of 3–5 mg, according to the patient’s weight. This was followed by application of xylocaine to the nasopharynx in a spray form. The endoscopic instrument that was used for the research was an Olympus gastroscope.

Histological examination of the tissue specimens was based on a Cresyl-Violet staining. In a small number of patients (5), who couldn’t be submitted to endoscopy due to lack of cooperation, we performed a serological examination of IgG antibodies against H.pylori.

Statistical analysis

The statistical analysis was based for the comparison of percentages on the x2 criterion. For the quantitative parameters the analysis was based on the non parametric Mann–Whitney-Wilcoxon test. The quantitative parameters were expressed as mean ± standard deviation. The levels for statistical significance were set for values of p < 0.05. The program we used for the statistical analysis was the SPSS 21.0 v.

Results and discussion

The study concluded to positive correlations between HP infection and dementia and H.pylori infection and glaucoma. This was expressed as an augmented frequency of H.pylori infection in the two groups in comparison to the frequency of the control group (68.33% in patients with dementia vs 45.16%, p < 0.05, 68.57% in patients with glaucoma vs 45.16%, p < 0.05). It has also shown a positive correlation between dementia and glaucoma, both in the form of augmented frequency of glaucoma in patients with AD and PD (16.66% vs 0%,) as well as in the form of augmented frequency of dementia (AD and FTD) in patients with glaucoma (16.66% vs 0%), in comparison to the frequency in the control group. The aforementioned findings are depicted in Tables 1, 2, 3, 4 and 5.

Table 1 Comparative data regarding age and gender between patients with dementia, glaucoma and the subjects of the 2 control groups
Full size table
Table 2 Helicobacter pylori infection in patients with dementia and control patients
Full size table
Table 3 Hp infection in glaucoma and control group patients
Full size table
Table 4 Frequency of glaucoma in patients with dementia – frequency of glaucoma in patients of the control group
Full size table
Table 5 Frequency of dementia in patients with glaucoma and control group
Full size table

The positive findings of the study in regard to the association of dementia (particularly AD) and Hp infection, POAG and H.pylori infection and finally, between dementia and POAG come to confirm the related conclusions reached by Kountouras et al. [9,11,12] and Bayer et al. [13].

Which common pathophysiological pathways stand behind the examined entities is not yet known. A possible explanation is that H.pylori infection initiates mechanisms of humoral and cellular immune response, which create crossreactions due to common genetic components with the ones found in nerve tissue; what follows are apoptosis-related mechanisms of cell destruction which are frequent in neurodegenerative diseases, such as dementia and glaucoma [31].

Another theory that might explain the findings of the study is that of the augmented permeability of the blood–brain barrier in patients with neurodegenerative diseases, such as multiple sclerosis [32,33]; this phenomenon may give to the H.pylori the chance to enter the barrier and accelerate or influence their course. Similarly, Deretzi et al. have recently [34] proposed a theory that H.pylori or other pathogens may follow a distinct pathway to bypass the blood–brain barrier and cause damage to the brain. More specifically, they use the gastrointestinal tract (GIT) retrograde axonal transport through sensory or motor fibres in order to invade the central nervous system.

The findings of the study may have important practical applications for our patients in the future. They may lead to a widely accepted eradication of H.pylori as a measure for prevention against dementia and glaucoma. They also may lead to the establishment of routine diagnostic examinations for glaucoma in patients with dementia and of dementia in patients with glaucoma, which would influence the quality of life of these patients positively. Continued research in this field in the epidemiological, but more intensely in the molecular level, might further clarify common biochemical pathways linking dementia, glaucoma and Hp infection.

Conclusions

  1. i.

    H.pylori infection is more frequent in patients suffering from AD and other forms of dementia than in the general population.

  2. ii.

    H.pylori infection is more frequent in patients suffering from POAG than in the general population.

  3. iii.

    POAG is more frequent in patients suffering from dementia (AD and PD) than in the general population.

  4. iv.

    Dementia (AD and FTD) is more frequent in patients with POAG than in the general population.