Homocysteine modifies the association of coronary stenosis and HIV infection in an inner city African American population

Abstract

Background and aims

People with HIV (PWH) whose disease is controlled on anti-retroviral regimens remain at an increased risk for coronary artery disease (CAD). Traditional cardiovascular risk factors do not fully explain the residual risk in PWH suggesting contributions from nontraditional factors. Homocysteine (Hcy) may be one of these as prior work in adults without HIV demonstrate that Hcy may impair endothelial function by decreasing the availability of nitric oxide, promoting the development of atherosclerosis. In addition, plasma Hcy levels are higher in PWH than in individuals living without HIV. The aim of this study was to investigate whether Hcy levels influence the association between HIV and coronary stenosis in an inner city African American population.

Methods

African Americans from the Heart Study in Baltimore, with and without HIV, recruited from inner-city Baltimore between June 2004 and February 2015, were included in this analysis. Participants underwent coronary CT angiography to evaluate the presence of coronary stenosis, defined as luminal stenosis >10%. Hcy was measured from stored serum samples.

Results

In this analysis, the median [IQR] age of the 664 participants was 56 [50–66] years; 68.1% were living with HIV and 43.1% were women. Elevated Hcy (>15 µmol/L) was more prevalent in those with coronary stenosis (23.3%, 95% CI: 18.4%–28.2%) than in those without coronary stenosis (13.1%, 95% CI: 9.7%–16.5%) (p = 0.0007), and HIV was associated with coronary stenosis in those participants with an elevated Hcy (Prevalence Ratio: 1.94, 95% CI: 1.04-3.64, p = 0.0038) and not in those with a Hcy ≤15 µmol/L (Prevalence Ratio: 1.02, 95% CI: 0.83-1.25, p = 0.87).

Conclusions

Our data suggest an association between elevated Hcy levels (>15 µmol/L) and the prevalence of coronary stenosis in PWH from this inner city African American population.

Keywords

Coronary stenosis HIV infection Homocysteine

Introduction

People living with HIV (PWH) are at an increased risk for premature atherosclerotic coronary artery disease (CAD) and subsequent cardiovascular events.¹ This increased risk remains despite significant improvements in anti-retroviral therapies that achieve an undetectable viral load in most people compliant with these therapies.² Traditional CAD risk factors are prevalent among PWH³; however, even after adjustment for traditional cardiovascular risk factor exposure, PWH experience a higher burden of atherosclerotic cardiovascular disease (ASCVD) and cardiovascular event rates than those without HIV,⁴ suggesting contributions from nontraditional factors. Coronary vascular endothelial cell dysfunction is the earliest marker of the atherosclerotic cascade and is prevalent in PWH.⁵ Many traditional, and previously described novel, CAD risk factors in PWH are associated with vascular endothelial dysfunction.⁶ Identifying additional modifiable risk factors may inform targeted interventions to mitigate the risk of atherosclerotic cardiovascular disease in PWH.

Increased homocysteine (Hcy) serum levels are associated with increased cardiovascular risk.⁷ Prior work in adults living without HIV demonstrated that Hcy, a sulfhydryl compound, may impair endothelial function by decreasing the bioavailability of nitric oxide (NO) through an autoxidation process in which the resulting superoxide anion reacts with NO to form peroxynitrite adducts and increase reactive oxygen species.^8,9 In vitro studies demonstrated direct endothelial cell injury related to Hcy concentrations.¹⁰ Homocysteine may be one of the modifiable CAD risk factors in PWH. Plasma Hcy levels are higher in PWH compared to individuals without HIV¹¹ and a direct association between Hcy and carotid intima-media thickness, an indicator of subclinical atherosclerosis, was previously reported in PWH.¹² However, the association of Hcy levels and coronary stenosis in PWH has not been characterized.

The objective of this investigation was to examine whether and, if so, to what extent elevated Hcy influences the association between coronary stenosis and HIV among an inner city African American population.

Participants and methods

Participants

The Heart Study in Baltimore is an observational study investigating the association of HIV infection, exposure to anti-retroviral therapies (ART), and ASCVD risk factors including cocaine use, with CAD in predominantly African American inner city individuals.¹³ The study enrolled 1429 African American men and women with and without HIV infection recruited between June 2004 and February 2015. It was designed so that 2/3 of those enrolled were PWH and 1/3 were people without HIV infection. Briefly, participants underwent assessments every 24 months, and these visits encompassed several components. All participants underwent HIV-infection testing through ELISA, with positive cases further confirmed by the Western blot test. Additionally, during the CTA examinations, biomarkers of inflammation, lipids, and supplementary serum samples for future analysis were collected. For participants living with HIV, comprehensive data on the duration of known HIV infection and medication details, including the use of nucleoside reverse-transcriptase inhibitors (NRTI), non-nucleoside reverse-transcriptase inhibitors (NNRTI), and protease inhibitors (PI), were collected. To ensure accuracy, a medical chart review was employed to corroborate the information pertaining to medical history and medications provided by the study participants. Exclusion criteria were (1) evidence of clinical CAD, (2) history of or current chronic obstructive pulmonary disease, (3) pregnancy or child-bearing potential and not using effective birth control measures, and (4) chronic kidney disease with an estimated glomerular filtration rate of <60 mL/minute/1.73 m². Detailed inclusion and exclusion criteria were previously published.¹⁴ PWH were recruited from the Johns Hopkins Adult HIV Clinic and participants without HIV were recruited from the local Baltimore communities. The Investigational Review Boards at the Johns Hopkins School of Medicine and the University of Maryland Baltimore approved the study protocol, and all study participants provided written informed consent.

Contrast-enhanced CCTA

Coronoray CT angiography (CCTA) scans were performed on a Siemens second-generation, 128-slice, dual-source CT (Somatom Definition Flash, Siemens Healthcare, Forchheim, Germany). The scan parameters were 100 kVp to 120 kVp (depending on the participant’s size), Care Dose quality reference standard of 320 mAs (Care Dose 4D was used to minimize the radiation dose), rotation time was 0.28 s, collimation was 128 x 0.6 mm, and average acquisition time was under 5 s (heart rate-dependent). Scan data were reconstructed with 0.75 mm thickness at 0.5 mm reconstruction spacing using a B26ASA and B30f reconstruction kernel with iterative reconstruction. The scan protocol used 80 mL to 100 mL of an iso-osmolar contrast agent (Vispaque-320, GE Medical Systems) injected at 5cc/s to 6 cc/s. Coronary plaque was defined as any discernible coronary artery wall thickening identified in at least two perpendicular imaging planes and causing at least a 10% reduction in lumen caliber.¹³ All images were interpreted by a board‐certified radiologist with additional board certification in cardiac CT interpretation. The reviewer was blinded to the participants’ characteristics, including HIV status.

Laboratory measures

Serum samples were obtained from study participants after an 8–12 h fast and the serum was separated using centrifugation and immediately stored at −80°C until further processing. Hcy levels and lipid profiles were obtained at the same time and measured at Quest Laboratories.

Statistical analysis

Statistical analysis was performed with the SAS software (version 9.4. SAS Institute, Cary, NC). All continuous parameters were summarized by medians with interquartile ranges (IQRs), and all categorical parameters were summarized as proportions. To compare between-group differences in demographic and clinical characteristics, lipid profiles, and other relevant factors, the nonparametric Wilcoxon rank-sum test was used for continuous variables and the chi-square test for categorical variables. The overall and group-specific prevalences of coronary stenosis and corresponding 95% confidence intervals were calculated.

Prevalence ratios derived from Poisson regression models were used to examine the associations between HIV and coronary stenosis. Univariable Poisson regression analyses were first performed to explore crude associations between coronary stenosis and each independent variable, including age >55 years (the median of age), sex, cigarette smoking, cocaine use, diabetes, body mass index (BMI), triglycerides, serum Hcy, and the Framingham 2013 ASCVD risk score (age, gender, systolic blood pressure, total cholesterol, HDL cholesterol, and cigarette use).¹⁵ Multivariable Poisson regression analyses, including all of the above mentioned variables were then performed to adjust for potential confounding factors. Elevated Hcy was defined as a plasma level of >15 μmol/L¹⁶ and was used in stratified Poisson regression analysis. The p-values reported are two-sided and a p-value of <0.05 indicated statistical significance.

Results

General characteristics of the study participants

Six hundred and sixty-four African American participants completed the CCTA exam and 649 had serum samples for the Hcy measurements. The median age was 56 years (IQR: 50–66 years), 43.1% were women, 68.1% were living with HIV, 49% had CCTA evidence of coronary stenosis, and 17.6% had elevated Hcy levels (>15 μmol/L). The general characteristics of the study participants are presented in Table 1. Table 2 presents the demographic, clinical, and laboratory characteristics of the study participants separated by HIV status.

Table 1.

Characteristics of African American adult study participants by coronary stenosis status^a.

Characteristic	All (N = 664)	Coronary stenosis (−) (N = 374)	Coronary stenosis (+) (N = 290)	p-value
Age	56 (50–60)	53(47–58)	59 (55–62)	<0.0001
Female sex % (n)	43.1 (286)	48.9 (183)	35.5 (103)	0.0005
Family history of CAD % (n)	26.7 (177)	23.5 (88)	30.7 (89)	0.04
Cigarette smoking % (n)				0.0001
Never	27.3 (181)	34.3 (125)	19.3 (52)
Current	56.2 (373)	50.1 (187)	64.1 (186)
Former	16.6 (110)	15.6 (62)	16.6 (48)
Chronic cocaine use % (n)	72.4 (481)	64.2 (240)	83.1 (241)	<0.0001
Alcohol use % (n)	83.0 (551)	82.1 (307)	84.1 (244)	0.49
Hypertension % (n)	25.2 (167)	23.0 (86)	27.9 (81)	0.15
Diabetes % (n)	7.8 (52)	5.1 (19)	11.4 (33)	0.003
BMI (kg/m²)	28.0 (23.0–33.0)	28.0 (24.0–34.0)	27.0 (23.0–32.0)	0.01
Systolic BP (mm Hg)	129 (118–140)	128 (117–139)	130 (119–141)	0.20
Diastolic BP (mm Hg)	73 (66–81)	73 (66–80)	73 (67–81)	0.33
hsCRP (mg/dL)	2.5 (0.9–6.6)	2.8 (0.9–6.7)	2.4 (1.0–6.5)	0.80
hsCRP ≥2 mg/mL (%)	55.8 (367)	57.1 (212)	54.0 (155)	0.42
Glucose (mg/dL)	87 (79–97)	86 (79–96)	87 (79–99)	0.21
Total cholesterol (mg/dL)	176 (151–205)	176 (151–203)	178 (151–207)	0.68
LDL-C (mg/dL)	96 (76–121)	94 (76–119)	97 (76–124)	0.30
HDL-C (mg/dL)	54 (43-66)	55 (44–68)	53 (43–63)	0.10
Triglycerides (mg/dL)	103 (74-147)	97 (71–140)	108 (77–157)	0.016
eGFR (mL/min/1.73 m²)	102 (89–119)	103 (91–119)	101 (85–117)	0.21
Homocysteine (µmol/L)	11 (9–14)	10 (8–13)	12 (10–15)	<0.0001
Homocysteine >15 (µmol/L)	17.6	13.1	23.3	0.0007
ASCVD risk (range)	10.3 (5.3–16.1)	7.2 (3.9–12.4)	13.4 (9.0–21.1)	<0.0001
Low ASCVD risk % (n)	37.2 (247)	51.3 (192)	19.0 (55)	<0.0001
HIV infection % (n)	68.1 (452)	65.0 (243)	72.1 (209)	0.05

Abbreviations: BMI: body mass index (kg/m²); hsCRP: high-sensitivity C-reactive protein; BP: blood pressure; LDL-C: low density lipoprotein cholesterol; HDL-C: high density lipoprotein cholesterol; glucose, fasting glucose; eGFR, estimated glomerular filtration rate; Framingham risk, Framingham risk score; ASCVD risk, cardiovascular risk defined by the 2013 ACC/AHA Guideline on the Assessment of Cardiovascular Risk; Low ASCVD risk, cardiovascular risk defined by the 2013 ACC/AHA Guideline on the Assessment of Cardiovascular Risk ≤7.5%.¹⁵

^aMedian (interquartile range) for continuous variables, proportion (%, n) for categorical variables.

Table 2.

Characteristics of African American adult study participants by HIV status^a.

Characteristic	All (N = 664)	HIV (−) (N = 212)	HIV (+) (N = 452)	p-value
Age	56 (50–60)	56 (50–60)	56 (51–61)	0.16
Female sex % (n)	43.1 (286)	48.1 (102)	40.7 (184)	0.07
Family history of CAD % (n)	26.7 (177)	28.8 (61)	25.7 (116)	0.40
Cigarette smoking % (n)				0.77
Never	27.2 (181)	27.4 (58)	27.2 (123)
Current	56.2 (373)	57.6 (122)	55.5 (251)
Former	16.6 (110)	15.1 (32)	17.3 (78)
Chronic cocaine use % (n)	72.4 (481)	67.0 (142)	75.0 (339)	0.03
Alcohol use % (n)	83.0 (551)	81.6 (173)	83.6 (378)	0.52
Hypertension % (n)	25.2 (167)	24.5 (52)	25.4 (115)	0.80
Diabetes % (n)	7.8 (52)	9.0 (19)	7.3 (33)	0.46
BMI (kg/m²)	28.0 (23.0–33.0)	29.0 (24.0–34.0)	27.0 (23.0–32.0)	0.01
Systolic BP (mm Hg)	129 (118–140)	130 (119–140)	129 (117–140)	0.15
Diastolic BP (mm Hg)	73 (66–81)	73 (67–79)	73 (66–81)	0.47
hsCRP (mg/dL)	2.5 (0.9–6.6)	2.3 (0.8–5.5)	2.8 (1.0–7.0)	0.14
hsCRP ≥2 mg/mL % (n)	55.8 (371)	53.1 (113)	57.0 (258)	0.36
Glucose (mg/dL)	87 (79–97)	86 (78–98)	87 (79–97)	0.75
Total cholesterol (mg/dL)	176 (151–205)	179 (154–204)	174 (147–205)	0.12
LDL-C (mg/dL)	96 (76–121)	98 (78–122)	94 (75–120)	0.17
HDL-C (mg/dL)	54 (43–66)	55 (45–67)	53 (43–65)	0.16
Triglycerides (mg/dL)	103 (74–147)	95 (67–142)	107 (77–152)	0.03
eGFR (mL/min/1.73 m²)	102 (89–119)	107 (95–126)	102 (87–118)	0.04
Homocysteine (µmol/L)	11 (9–14)	10 (8–13)	11 (9–14)	0.001
Homocysteine >15 (µmol/L) % (n)	17.6 (116)	10.1 (21)	21.0 (95)	0.0007
ASCVD risk (%)	10.3 (5.3–16.1)	9.0 (5.1–15.7)	10.8 (5.3–16.5)	0.28
Low ASCVD risk % (n)	37.2 (247)	41.0 (87)	35.4 (160)	0.16
Coronary stenosis % (n)	43.7 (290)	38.2 (81)	46.2 (209)	0.052

^aMedian (interquartile range) for continuous variables, proportion (%, n) for categorical variables.

Factors associated with the presence of coronary stenosis

In the entire cohort, multivariable Poisson regression analysis demonstrated that age >55 years (adj prevalence ratio: 1.75, 95% CI: 1.36-2.25, p < 0.0001), chronic cocaine use (adj prevalence ratio: 1.38, 95% CI: 1.07-1.78, p = 0.014) and ASCVD risk (adj prevalence ratio: 5.64, 95% CI: 2.32-13.70, p = 0.0001) were independently associated with the presence of coronary stenosis, while HIV (p = 0.22) and elevated Hcy (>15 μmol/L) were not (p = 0.26) (Table 3).

Table 3.

Factors associated with the presence of coronary stenosis.

Characteristic	Univariable		Multivariable
Characteristic	PR (95% CI)	p-value	PR (95%CI)	p-value
Age >55 years	2.39 (1.91, 2.97)	<0.0001	1.75 (1.36, 2.25)	<0.0001
Female sex	0.73 (0.61, 0.88)	0.0009	0.94 (0.78, 1.13)	0.50
Family history of CAD	1.16 (1.06, 1.27)	0.0008	1.09 (0.99, 1.19)	0.07
Cigarette smoking
Never	Reference		Reference
Current	1.61 (1.26, 2.05)	0.0001	1.20 (0.93, 1.55)	0.15
Former	1.41 (1.04, 1.92)	0.03	0.97 (0.71, 1.55)	0.83
Cocaine use	1.87 (1.45, 2.41)	<0.0001	1.38 (1.07, 1.78)	0.014
Diabetes	1.51 (1.21, 1.89)	0.0003	1.01 (0.63, 1.62)	0.97
BMI (kg/m²)	0.98 (0.97, 0.99)	0.009	0.99 (0.98, 1.01)	0.13
Glucose (mg/dL)	1.00 (1.00, 1.00)	0.004	1.00 (0.99, 1.01)	0.85
LDL-C (mg/dL)	1.00 (0.99, 1.00)	0.28	1.00 (0.99, 1.00)	0.07
HDL-C (mg/dL)	0.99 (0.99, 1.00)	0.050	0.99 (0.99, 1.00)	0.09
Triglycerides (mg/dL)	1.00 (0.99, 1.00)	0.15	0.99 (0.99, 1.00)	0.57
Homocysteine >15 (µmol/L)	1.40 (1.18, 1.73)	0.0003	1.12 (0.92, 1.35)	0.26
ASCVD risk (%)	32.98 (17.46, 62.18)	<0.0001	5.64 (2.32, 13.70)	0.0001
HIV infection	1.21 (0.99, 1.48)	0.055	1.13 (0.93, 1.35)	0.22

Abbreviations: PR: prevalence ratio; 95% CI: 95% confidence interval; BMI: body mass index (kg/m²); glucose, fasting glucose; LDL-C: low-density lipoprotein cholesterol; HDL-C: high-density lipoprotein cholesterol; ASCVD risk, atherosclerotic cardiovascular disease risk defined by the 2013 ACC/AHA Guideline on the Assessment of Cardiovascular Risk.¹⁵

Associations between HIV and coronary stenosis by elevated Hcy level (>15 μmol/L)

Although multivariable Poisson regression analysis indicated that HIV was not associated with coronary stenosis among those participants with Hcy levels ≤15 μmol/L (adj prevalence ratio: 1.02, 95% CI: 0.83-1.25, p = 0.87), HIV was independently associated with the presence of coronary stenosis in those participants with Hcy of >15 μmol/L (adj prevalence ratio: 1.94, 95% CI: 1.02-3.64, p = 0.038) (Table 4).

Table 4.

Factors associated with the presence of coronary stenosis stratified by homocysteine level of <15 μmol/L or >15 μmol/L.

Characteristic	Univariable		Multivariable
Characteristic	PR (95% CI)	p-value	PR (95% CI)	p-value
Homocysteine ≤15 µmol/L
Age >55 years	2.49 (1.94, 3.20)	<0.0001	1.93 (1.44, 2.58)	<0.0001
Female sex	0.73 (0.59, 0.90)	0.004	0.89 (0.72, 110)	0.28
Family history of CAD	1.17 (1.07, 1.28)	0.0006	1.09 (0.99, 1.21)	0.07
Cigarette smoking
Never	Reference		Reference
Current	1.61 (1.21, 2.15)	0.001	1.25 (0.93, 1.68)	0.14
Former	1.47 (1.02, 2.10)	0.04	0.99 (0.68, 1.45)	0.97
Cocaine use	1.85 (1.38, 2.49)	<0.0001	1.36 (1.01, 1.82)	0.04
Diabetes	1.68 (1.31, 2.17)	<0.0001	1.24 (0.76, 2.01)	0.39
BMI (kg/m²)	0.99 (0.97, 1.01)	0.06	0.99 (0.97, 1.01)	0.26
Glucose (mg/dL)	1.00 (1.00, 1.01)	0.005	0.99 (0.99, 1.01)	0.56
LDL-C (mg/dL)	1.00 (0.99, 1.00)	0.89	1.00 (0.99, 1.01)	0.33
HDL-C (mg/dL)	0.99 (0.98, 1.00)	0.19	0.99 (0.98, 1.00)	0.22
Triglycerides (mg/dL)	1.00 (0.99, 1.00)	0.18	0.99 (0.99, 1.00)	0.47
ASCVD risk (%)	38.26 (18.17, 79.84)	<0.0001	5.21 (1.65, 16.44)	0.005
HIV infection	1.01 (0.86, 1.33)	0.52	1.02 (0.83, 1.25)	0.87
Homocysteine>15 µmol/L
Age >55 years	1.40 (0.89, 2.20)	0.15	1.06 (0.69, 1.64)	0.79
Female sex	0.88 (0.61, 1.27)	0.50	1.30 (0.89, 1.90)	0.17
Family history of CAD	1.02 (0.73, 1.43)	0.90	1.17 (0.83, 1.64)	0.37
Cigarette smoking
Never	Reference		Reference
Current	1.56 (1.00, 2.44)	0.049	1.05 (0.67, 1.65)	0.84
Former	1.15 (0.64, 2.08)	0.63	0.87 (0.51, 1.49)	0.62
Cocaine use	1.82 (1.08, 3.06)	0.02	1.60 (0.94, 2.71)	0.08
Diabetes	0.93 (0.53, 1.65)	0.82	0.70 (0.24, 2.03)	0.51
BMI (kg/m²)	0.99 (0.97, 1.01)	0.31	0.97 (0.94, 1.00)	0.05
Glucose (mg/dL)	1.00 (0.99, 1.00)	0.77	1.00 (0.99, 1.01)	0.23
LDL-C (mg/dL)	1.00 (1.00, 1.01)	0.02	1.00 (0.99, 1.01)	0.12
HDL-C (mg/dL)	0.99 (0.98, 0.99)	0.04	0.99 (0.98, 0.99)	0.04
Triglycerides (mg/dL)	0.99 (0.99, 1.00)	0.98	0.99 (0.99, 1.01)	0.54
ASCVD risk (%)	10.70 (2.61, 43.38)	0.001	6.17 (1.51, 25.28)	0.01
HIV infection	1.64 (0.93, 2.89)	0.09	1.94 (1.04, 3.64)	0.038

Discussion

The findings of this study indicate that homocysteine modifies the association of coronary stenosis and HIV infection in an inner city African American population; HIV was independently associated with the presence of coronary stenosis among those participants with Hcy levels >15 μmol/L, and not among those with Hcy levels ≤15 μmol/L.

HIV is a chronic inflammatory condition and the direct inflammatory response from the virus itself may importantly contribute to vascular damage and accelerated ASCVD in PWH. In addition, traditional inflammatory mediators such as chemokines and cytokines as well as novel inflammatory mediators, e.g., proprotein convertase subtilisin/kexin type 9 (PCSK9), are present in PWH, are associated with vascular dysfunction,⁵ and inhibition of PCSK9, another inflammatory mediator, improves coronary vascular endothelial cell function, a barometer of vascular health, in people with HIV.⁶

A statement for healthcare professionals from the Nutrition Committee of the American Heart Association established Hcy levels of 5 µmol/L −15 µmol/L as the normal range¹⁶ and elevated Hcy levels are reported to be an independent risk factor for vascular disease in individuals without HIV.¹⁷ Several mechanisms for the increased cardiovascular risk of Hcy have been proposed, including vascular endoplasmic reticulum dysfunction and vascular injury,¹⁸ direct endothelial cell injury, and decreased NO bioavailability,¹⁹ as well as increased oxidative stress and inflammatory cytokine signaling.¹⁸ An in vitro study in human aortic endothelial cells showed that Hcy impairs endothelial cell function via inflammatory signaling through increased MCP-1 and IL-8 expression and secretion.²⁰

A meta-analysis showed that plasma Hcy levels are higher, by an average of 2.05 µmol/L (95% CI: 0.10 - 4.00, p < 0.01) in PWH than in individuals without HIV.¹¹ Elevated Hcy in PWH may be attributed to a variety of factors related to B-vitamin deficiencies. Malnutrition in PWH is well described and is likely multifactorial, including reduced appetite secondary to depression and to ART, infection-induced diarrheal illnesses, viral-induced damage to intestinal villi, and social economic factors.²¹ Vitamins B6 (pyridoxine), B9 (folate) and B12 (cobalamine) function as cofactors or substrates in the methionine-homocysteine metabolic pathway. As such, there are inverse associations between Hcy and B-vitamin concentrations.²² In a cohort of over 1000 individuals not living with HIV from the original Framingham Heart Study, subnormal plasma concentrations of at least one of the three B-vitamins were present in two-thirds of individuals with elevated Hcy.²³

Elevated Hcy levels are a risk factor for subclinical cerebrovascular disease in PWH. In a 423-patient multicenter prospective study that evaluated PWH, a linear relationship between Hcy and carotid intima-media thickness was demonstrated.¹² Furthermore, a meta-analysis including 12 prospective studies showed that, after adjusting for known CAD risk factors, Hcy levels were directly associated with the risks of strokes and ischemic heart disease events.²⁴ Additionally, including novel cardiovascular mediators, e.g., Hcy, in cardiovascular risk assessment tools based on traditional cardiovascular disease risk factors alone, e.g. the Framingham Risk Score, significantly improves risk classification in HIV-negative individuals.²⁵ The pathophysiology underlying CAD in PWH likely involves traditional risk factors, infection-related and ART-related factors, as well as other non-traditional risk factors.²⁶ Our results indicate that HIV is independently associated with the presence of coronary stenosis among those participants with Hcy levels >15 μmol/L, but not among those with Hcy levels ≤15 μmol/L.

There is evidence to suggest that there may be differences in Hcy levels among different racial and ethnic groups. For example, some studies found that African Americans tend to have higher Hcy levels than other racial and ethnic groups.^27,28 However, elevated levels of Hcy are associated with an increased risk of cardiovascular disease regardless of race or ethnicity. A genome-wide association study for Hcy including 4927 African Americans from the Jackson Heart Study, the Multi-Ethnic Study of Atherosclerosis, and the Coronary Artery Risk in Young Adults Study found that African Americans had a higher prevalence of certain genetic variants associated with Hcy metabolism compared to Caucasians, but a lower prevalence of other variants.²⁹ The study also found that the overall variance in Hcy levels that could be explained by the combined presence of these genetic variants increased slightly over time in both Caucasians and African Americans. Therefore, African Americans may be at a higher risk for ASCVD due to the higher prevalence of certain genetic variants associated with Hcy metabolism.

Interventions to improve cardiovascular outcomes by reducing plasma Hcy levels were previously tested. A Cochrane review included 15 randomized controlled trials and concluded that Hcy-lowering interventions in the form of supplements of vitamins B6, B9, or B12 given alone or in combination, did not decrease myocardial infarction or death outcomes.³⁰ However, these interventions did reduce the stroke outcome (Hcy-lowering = 4.3% vs. comparator = 5.1%, relative risk 0.90, 95% CI [0.82 - 0.99].³⁰ It is important to note that an elevated plasma Hcy at baseline was not required in any of these trials, and none included PWH. Our results indicate that Hcy modifies the association of coronary stenosis and HIV infection in an inner city African American population. Given the strong relationship between HIV, Hcy, and coronary stenosis in our analysis, clinical trials studying the effect of interventions that lower Hcy on subclinical and clinical coronary disease in this population are needed.

Our study has several important limitations: (1) this investigation is a cross-sectional analysis, and although we explored whether HIV was associated with the presence of coronary stenosis, we have no knowledge as to whether coronary stenosis was present prior to HIV acquisition; (2) serum samples for the Hcy measures were obtained within 2 years, but not all at the same time as the CT scans, (3) we are reporting associations and not causation relationships; (4) our study was conducted in an inner-city African American population with a high prevalence of substance use and the results may not be generalizable to other populations; and (5) this study did not include measures of B-vitamin levels. Longitudinal and intervention studies are needed to address some of these limitations.

In conclusion, our data suggest that elevated Hcy moderates the association between HIV and coronary artery stenosis among the inner-city African American Heart Study participants. This finding may prompt further investigation regarding the responsible mechanisms and therapeutic interventions in people with HIV. The findings from this study also emphasize the crucial need to recognize and understand the influence of non-HIV factors on the presence of HIV-related cardiovascular comorbidities.

Footnotes

Author contributions

TML, GG, TH, EZ, SL, and HL: drafting the work and reviewing it critically for important intellectual content. GG, DDC, GT, SL, and HL: substantial contributions to the conception or design of the work. SL and HL performed data analysis and interpretation of data. TML, GG, DDC, TH, EZ, GT, RNM, JK, MC, SL and HL: reviewing the manuscript critically for important intellectual content and final approval of the version to be published. SL: agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

Research reported in this publication was supported by grants from the US National Institute on Drug Abuse, National Institutes of Health (NIH R01DA12777, R01DA15020, R01DA25524, R01DA035632, R21DA048780, and U01DA040325).

ORCID iDs

Thorsten M Leucker

Jag Khalsa

Shenghan Lai

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