The purpose of this study is to explore a possible link between the autonomic nervous system and immune function in patients with HIV. Sometimes HIV can cause these nerves to function abnormally, this is called HIV-associated autonomic neuropathy (HIV-AN). HIV-AN is a condition that is different from person to person. In some people it causes no symptoms and is not harmful, in others it may cause symptoms such as dizziness or lightheadedness, nausea, vomiting, diarrhea, constipation, or problems urinating. Most people with HIV-AN don't know that they have it. One of the important nerves in the autonomic nervous system is the vagus nerve. Abnormal function of the vagus nerve may cause stomach and intestinal slowing, which could lead to an overgrowth of bacteria. The body senses these bacteria and tries to fight them, leading to inflammation.

In this study the researchers will test whether abnormal function of the vagus nerve in HIV is associated with stomach slowing and overgrowth of bacteria, and if a drug called pyridostigmine can help.

HIV-infected patients commonly develop autonomic neuropathy (HIV-AN), which is a heterogeneous disorder characterized by varying degrees of both sympathetic and vagal dysfunction. We hypothesize that the vagal component of HIV-AN contributes to chronic inflammation, both directly via loss of cholinergic activity, and indirectly via effects on the GI tract, and that these effects will be treatable using the acetylcholinesterase inhibitor pyridostigmine. The autonomic nervous system controls the inflammatory response to lipopolysaccharide (LPS) via the cholinergic anti-inflammatory pathway. This pathway is mediated by the vagus nerve, and is therefore likely impaired in HIV-AN with vagal dysfunction. Vagal dysfunction also causes slowed GI transit, which could exacerbate LPS-driven inflammation by promoting bacterial overgrowth. However, the anti-inflammatory impact of cholinergic pathways is almost completely unstudied in HIV, despite the known importance of inflammation in HIV disease progression. Therefore, in this exploratory pilot, we seek to establish associations between vagal dysfunction, GI motility and inflammation in virally suppressed, CART-treated individuals with HIV-AN.

Specific Aim 1: To determine whether vagal dysfunction is associated with immune activation in CART-treated participants with HIV-AN, and if so to estimate the extent to which this association is mediated by GI effects (i.e. slowed motility, bacterial overgrowth, microbial translocation) versus direct effects of vagal dysfunction.

Specific Aim 2: In a subset of participants who have both vagal and GI dysfunction, to investigate whether 8 weeks of pyridostigmine: a) reduces immune activation, and b) improves GI motility; and if the immune effect depends on the GI effect.

To achieve these aims, participants with HIV-AN and GI symptoms will be assessed for: vagal dysfunction (heart rate variability); GI dysmotility (gastric emptying scintigraphy); small intestinal bacterial overgrowth (breath testing); microbial translocation (LPS and sCD14); and immune activation (IL-6 and CRP). Participants meeting threshold criteria for both vagal and GI dysfunction will then be treated with pyridostigmine for 8 weeks, after which GI and immune measures will be reassessed.

Objectives Specific Aim 1: To determine whether vagal dysfunction is associated with immune activation in HIV-infected participants treated with combination antiretroviral therapy (CART), and if so to estimate the extent to which this association is mediated by GI effects (i.e. slowed motility, bacterial overgrowth, microbial translocation) versus direct effects of vagal dysfunction.

Specific Aim 2: In a subset of participants who have both vagal and GI dysfunction, to investigate whether 8 weeks of pyridostigmine: a) reduces immune activation, and b) improves GI motility; and if both effects are present to determine whether the immune effect depends on the GI effect.

Inclusion Criteria:

• ≥18 years old
• Documented evidence of HIV-1 infection
• Stable CART therapy for ≥3 months Most recent HIV-1 viral load ≤100 copies/ml (value must be within the past six months)
• English speaking
• Able to tolerate autonomic testing (e.g. able to stand, able to perform Valsalva maneuver).
• If using nicotine-containing products willing to refrain from use for 24 hours prior to all testing procedures (autonomic reflex screen, breath testing, and gastric emptying)
• ≥1 GI symptom on the Survey of Autonomic Symptoms (SAS)47

Exclusion Criteria:

• Diagnosis known to cause autonomic dysfunction other than HIV (e.g. Parkinson's disease, diabetes)
• Diagnosis known to cause GI dysfunction other than HIV (e.g. peptic ulcer disease, infectious diarrhea)
• Current use of any of the following classes of medications (due to potential for significant autonomic or GI effects, interaction with pyridostigmine, or interference with one or more of the testing procedures) Prokinetics (e.g. metoclopramide) Anti-diarrheals (e.g. loperamide) Antibiotics Mefloquine
• Medical or psychiatric conditions precluding safe participation in study procedures or deemed likely to result in hospitalization during the study period.
• The presence of one or more of the following diagnoses which render the Valsalva maneuver relatively or absolutely contraindicated: uncontrolled glaucoma, aortic stenosis, myocardial infarction in the last 6 months, other retinopathy or unclipped cerebral aneurysm.
• The presence of one or more of the following diagnoses which impede interpretation of autonomic testing: cardiac arrhythmias or pacemakers.
• An allergy to eggs (contraindication to gastric emptying scintigraphy)
• Any of the following laboratory results:

Positive pregnancy test (administered to women of childbearing potential only) Urine toxicology screen positive for stimulants (e.g. amphetamines, cocaine) or opiates/opioids.

Data will be shared with participants in real time if the tests have any clinical significance.

8 weeks

Limitations include difficulty with recruitment resulting in small sample size, and lack of placebo control.