Investigation of the correlation of adropin with anthropological and psychological factors in schizophrenia: preliminary evidence from a case-control study

This preliminary case-control study found no significant difference in adropin levels between patients with schizophrenia and healthy volunteers, though it identified several notable correlations between adropin, anthropometric, and psychological factors that warrant further investigation.

The Gist

The Big Picture: A Detective Story in the Brain

Imagine the human brain as a bustling city. In people with Schizophrenia, the city's traffic lights are flickering, the power grid is unstable, and the citizens (the patients) are struggling to navigate their daily lives. For decades, doctors have been trying to figure out why the power grid is failing. They've looked at the main wires (neurotransmitters like dopamine) and found some clues, but the whole picture is still blurry.

In this study, a team of researchers from Japan decided to investigate a new, tiny "energy manager" in the city called Adropin.

What is Adropin?
Think of Adropin as a smart thermostat for the body's energy. It helps regulate how much fuel the cells burn, protects the cells from rust (oxidation), and keeps the brain's wiring safe. The researchers wondered: Is this thermostat broken in the city of Schizophrenia?

The Investigation: Comparing Two Neighborhoods

The researchers set up a small-scale investigation (a "case-control study") comparing two groups:

1. The Healthy Neighborhood (HV): 10 people with no mental health issues.
2. The Schizophrenia Neighborhood (SZ): 10 patients currently hospitalized for schizophrenia.

They didn't just look at the thermostat (Adropin). They also checked the "vital signs" of the city:

• Physical strength: How hard could they squeeze a handgrip? (Like checking the strength of the city's construction crew).
• Mental weather: How stressed, anxious, or sleepy did they feel? (Checking the mood of the citizens).
• Fuel levels: They tested their blood for minerals like Selenium and Iron (Ferritin), which are like the coal and oil keeping the city running.

The Findings: What the Data Said

1. The Thermostat is Working (Mostly)
The big surprise? The Adropin levels were exactly the same in both groups. The "thermostat" wasn't broken or turned off in the Schizophrenia group. This suggests that Schizophrenia isn't caused by a total lack of this specific energy manager.

2. The "Handshake" Mystery
Here is where it gets interesting. The researchers looked for connections between different variables, like seeing if two things move together.

• The Strong Grip: In healthy people, your left and right handgrip strength usually go up and down together (if one is strong, the other is too). In the Schizophrenia group, this connection was weaker. It's like the construction crew on the left side of the city isn't talking to the crew on the right side anymore.
• The Adropin-Grip Link: In the Schizophrenia group, there was a strange, strong link between Adropin and the right handgrip strength. When Adropin went up, the grip went down. This didn't happen in healthy people. It's as if, in the Schizophrenia city, the energy manager is strangely tied to how strong the workers can squeeze their hands.

3. The Selenium and Anxiety Connection
They found a link between Selenium (a mineral) and Anxiety. In the Schizophrenia group, higher Selenium levels seemed to go hand-in-hand with higher anxiety.

• The Analogy: Imagine Selenium is a spice. A little bit makes the food (the brain) taste great and protects it. But maybe, in this specific city, too much of this spice is making the citizens jittery and anxious.

4. Stress and Iron
They also noticed that when people felt more Stress, their Iron (Ferritin) levels tended to drop. It's like stress is a leaky faucet draining the city's iron reserves.

Why Does This Matter? (The Takeaway)

This study is like finding a new map for a territory that was previously dark.

• The Good News: We know the "Adropin thermostat" itself isn't broken.
• The Clue: The relationship between Adropin and physical strength is different in Schizophrenia. This suggests that while the thermostat works, the way it talks to the rest of the body (specifically the muscles and nerves) might be out of sync.
• The Future: Even though this was a small study (only 20 people total), it gives scientists a new direction. Instead of just looking at "broken wires," they might need to look at how the brain's energy manager talks to the body's muscles and how minerals like Selenium affect anxiety.

The Caveats (The "Fine Print")

The researchers were very honest about the limitations:

• Small Sample Size: It's like trying to predict the weather for a whole country by only looking at two towns. They need more data.
• Hospitalized Patients: All the patients were in the hospital, which might have affected their stress levels or physical activity.
• Men Only: The study only included men, so we don't know if this applies to women.

In a Nutshell

This study didn't find a "cure," but it found a new clue. It suggests that in Schizophrenia, the body's energy management system (Adropin) is interacting strangely with physical strength and anxiety. It's a preliminary step, but it lights a small lantern in a very dark room, helping future researchers know where to look next.

Technical Summary

1. Problem Statement and Hypothesis

Background: Schizophrenia is a severe, lifelong mental disorder with complex pathophysiology involving neurotransmitter dysfunction (dopamine, glutamate) and emerging evidence of brain energy metabolism deficits. Antipsychotic medications can impair mitochondrial function, leading to ATP depletion and oxidative stress.
The Gap: While adropin (a 76-amino acid peptide encoded by the ENHO gene) is known to regulate energy homeostasis, antioxidation, and neuroprotection, its specific role and correlation with anthropological and psychological factors in schizophrenia have not been investigated in human or animal models.
Hypothesis: The authors hypothesized that adropin levels might differ between patients with schizophrenia spectrum disorders and healthy volunteers, and that adropin levels would correlate with specific anthropological (e.g., handgrip strength) and psychological (e.g., anxiety, stress) factors, potentially offering a new therapeutic target.

2. Methodology

Study Design: An observational case-control study conducted at Kagoshima University Hospital and Nishida Hospital, Japan.
Participants:

• Total N: 20 participants (10 Healthy Volunteers [HV], 10 Patients with Schizophrenia Spectrum Disorders [SZ]).
• Inclusion Criteria: Diagnosed with schizophrenia, schizoaffective disorder, or schizophreniform disorder (DSM-5); aged 45–65; voluntary participation.
• Exclusion: Severe psychotic symptoms preventing participation.
• Demographics: All participants were male (a noted limitation). One SZ participant had comorbid diabetes mellitus.
  Data Collection:
• Anthropological: Height, weight, right handgrip strength (grip_R), left handgrip strength (grip_L).
• Psychological: Zung Self-Rating Depression Scale (SDS), State-Trait Anxiety Inventory (STAI), Trait Emotional Intelligence Questionnaire (TEIQue-SF), Pittsburgh Sleep Quality Index (PSQI), Perceived Stress Scale (PSS), and Apathy Scale (AS).
• Psychiatric (SZ only): Positive and Negative Syndrome Scale (PANSS) and medication dosage (chlorpromazine equivalents).
• Laboratory: Serum levels of Adropin (ELISA), Calcium, Copper, Iron, Selenium, Zinc, Vitamins A/B1, and Ferritin.
  Statistical Analysis:
• Software: Python (pandas, statsmodels, seaborn, matplotlib).
• Tests: Mann-Whitney U test for group differences (with Bonferroni correction); Kendall's tau ($\tau$) for correlation analysis.
• Correction: False Discovery Rate (FDR) applied for correlations (threshold $\alpha = 0.1$ for detection, $\alpha = 0.05$ for group differences).

3. Key Results

Group Comparisons (HV vs. SZ):

• Adropin Levels: No significant difference was found between HV and SZ groups. The levels were consistent with previous literature using the same ELISA kits.
• Significant Differences: PSQI (sleep quality), PSS (perceived stress), and right handgrip strength (grip_R) were significantly different between groups.

Correlation Analysis (Kendall's Tau):
The study identified five significant correlations (or near-significant trends) after correcting for natural proportional relationships:

1. Adropin vs. Right Handgrip Strength (grip_R):
   • SZ Group: Strong negative correlation ($\tau = -0.82, P = 0.066$).
   • HV Group: No correlation ($\tau = 0.16$).
   • Group Difference: The difference in correlation coefficients was statistically significant ($\tau_{diff} = -0.98, P = 0.013$).
2. Selenium vs. State Anxiety (STAI_S):
   • Total Group: Positive correlation ($\tau = 0.44, P = 0.053$).
   • SZ Group: Strong positive correlation ($\tau = 0.84, P = 0.066$).
3. Ferritin vs. Perceived Stress (PSS):
   • Total Group: Negative correlation ($\tau = -0.44, P = 0.053$).
4. Right vs. Left Handgrip Strength:
   • Total Group: Strong positive correlation ($\tau = 0.70, P = 0.001$).
   • SZ Group: Positive but non-significant trend ($\tau = 0.64, P = 0.137$).
5. Adropin vs. Selenium:
   • Total Group: Positive correlation ($\tau = 0.44, P = 0.053$).

4. Key Contributions and Interpretations

• Adropin as a Biomarker: The study provides the first evidence that serum adropin levels are not altered in schizophrenia patients compared to healthy controls, suggesting that the disease state itself does not dysregulate systemic adropin production, even though its function may be relevant.
• Novel Correlation (Adropin & Muscle Strength): A unique finding is the significant negative correlation between adropin and right handgrip strength specifically in the SZ group. The authors speculate this may be mediated by:
  • NB-3/Notch1 signaling: Adropin's known role in locomotor activity in rodents.
  • Dopamine Interaction: Potential structural similarity between the adropin receptor (GPR19) and Dopamine D2 receptors, suggesting adropin might be modulated by dopaminergic dysregulation or antipsychotic treatment.
• Selenium and Anxiety: The positive correlation between selenium and state anxiety in SZ patients challenges the common view that low selenium is solely detrimental. The authors suggest that in the context of the Japanese population (where baseline selenium is high), elevated selenium might be associated with transient anxiety or oxidative stress responses.
• Ferritin and Stress: The negative correlation between ferritin and perceived stress aligns with literature suggesting stress may deplete iron stores or that low iron exacerbates stress responses.

5. Significance and Limitations

Significance:

• This study shifts the focus from adropin levels to adropin functionality and its relationship with physical and psychological markers in schizophrenia.
• It establishes a foundation for investigating adropin as a potential therapeutic target, particularly regarding energy metabolism and neuromuscular function in schizophrenia.
• It highlights the complex interplay between trace elements (selenium, ferritin), stress, and anxiety in this patient population.

Limitations:

• Sample Size: Very small (N=20), leading to low statistical power and potential Type II errors.
• Demographics: All participants were male; results may not generalize to women.
• Setting: All SZ patients were hospitalized, which may introduce environmental bias regarding physical activity and stress levels.
• Comorbidities: One SZ participant had diabetes, a condition known to affect adropin levels, though the study notes this as a potential confounder.
• Preliminary Nature: The authors explicitly state this is a preliminary study not yet peer-reviewed, intended to guide future larger-scale research.

Conclusion:
While adropin levels do not differ between schizophrenia patients and healthy controls, the peptide shows a distinct, negative correlation with handgrip strength in patients. This suggests adropin may play a role in the physical and metabolic manifestations of schizophrenia, warranting further investigation into its mechanisms involving dopamine pathways and energy homeostasis.