Electrophoretic Light Scattering Studies of Virus (HIV) Charge Interactions

Another decade another deadly virus. In 2005 the genetic content of the HIV virus as well as its biological activity, structure and reactivity of its surface constituents had been extensively studied.

However, by 2005 the face of this pandemic was shifting, a higher percentage of new infections were being identified due to heterosexual contact. Approximately 40 Million people were living with HIV.

• In South Africa, one in four women were being infected with HIV by age 22.
• Sub-Saharan Africa 57% of adults aged 15-49 were infected with HIV.
• Southeast Asia, the Mekong Region, 30% of the new infections were occurring in women.
• India, 22% of cases were occurring in housewives and single partner relationships. 

Fifteen years ago, enough was understood about HIV-1 that a preventative vaccine was considered a long-term prospect. Therefore, in addition to vaccine research, three other paths were pursued to help reduce the spread of HIV around the world; 1.) membrane disruptive agents that would destroy the outer envelope layer of the virus; 2.) charge-dependent inhibition of viral attachment/fusion which was an appealing strategy because this would be an inexpensive solution and the virus would be stopped in the vaginal lumen, a highly biocompatible approach; 3.) antiviral drugs that would mirror those used in HIV therapy which were expensive, highly potent and could possibly introduce resistance problems.

Under the umbrella of the International Partnership for Microbicides (IPM), Professor Robin Shattock (Imperial College London) at St George’s Hospital London focused on the second strategy, pursuing a low cost “charge dependent” microbicide solution that could be made available to protect women and men from HIV infection. Also a research group at Magee Women’s Research Institute in Pittsburgh under Professors Sharon Hillier and Lisa Rohan worked to develop the microbicide.

The basic premise behind the “charge-based” strategy was to either prevent attachment by blocking, shielding or repulsion between the virus and the cell attachment sites. The virus carries a net negative charge as do the cells. The free virus first attaches via the CD4 binding site of the gp120 envelope protein, then fuses with the cell.  However, the gp120 undergoes a conformational change on approach of the virus to the cell that allows the gp120 to attach to what are termed the CCR5 receptors on the cell membrane.

Studies began in pursuing polyanion microbicides, based on the premise that this chemistry would bind to a sterically-restricted surface on the viral envelope (gp120 that conforms to carry a positive charge). The objective was to inhibit the virus-cell interaction and prevent HIV-1 from entering cells so that it became, effectively, an inert particle.

The surface physicochemical properties were evaluated using electrophoretic mobility (zeta potential).  Since cells and viruses can have different “activity”, mapping the topography of the “particle” provided insight to unraveling interaction mechanisms. 

The initial electrophoretic studies were performed using three human CD4+ T cell lines (H9, C8166 and Molt 4) each permissive for HIV-1 replication. The studies were carried out at pH and ionic strength conditions that covered the range relevant for infection which included; 1.) the vaginal environment pre- and post-intercourse, 2.) vaginal fluid, pH 4.0-6.5 and 3.) seminal fluid, pH 6.5-8.5.

The below results indicate a topographical titration study of electrophoretic mobility data obtained for C8166 cells in a range of ionic strength and pH, again this specific data was obtained for C8166 cells, but the same behavior was found for H9 and Molt4 cells.

Titration data of electrophoretic mobility studies on gp120 (the dominant protein on the HIV envelope and a key to its infectivity) are shown in Figure 2. Here at around pH 7 (on the upscale sweep) it suddenly becomes positive. This same pH change occurs in-vivo when ejaculate is introduced into the vagina, the moment of male-to-female transmission of the virus.

Electrophoretic mobility (zeta potential) studies generated information about cell surface chemistry and HIV infectivity. Specifically, T-cells are relatively neutral to slightly negatively charged in the pH region of vaginal fluid. Also, T-cells become more negatively charged during the pH region of interaction with semenal fluid. However, the electrophoretic mobility zeta potential of GP-120/140 becomes cationic, between pH 6-8.5, the ideal surface interaction for infectivity. This electrophoretic mobility data generated important information concerning the relation of cell surface chemistry and HIV infectivity.

After three decades of HIV research a vaccine has yet to be discovered. Microbicide product was developed and Gilead Sciences started producing the product in 2011. Currently, specific antiviral drugs/cocktails help HIV patients, but 65 million deaths have occurred due to AIDS.

Zeta potential has been used for decades to optimize vaccine adjuvants and virus research. The above HIV example is the first use of electrophoretic mobility (zeta potential) to help with the understanding of the potential electrostatic interactions between the glycoprotein envelope of HIV and its attachment to human T-cells. 

Further reading

• Microbicides for HIV/AIDS. 1. Electrophoretic Fingerprinting the H9 Cell Model System
• Microbicides for HIV/AIDS. 2. Electrophoretic fingerprinting of CD4+T-cell model systems
• Microbicides for HIV/AIDS. 3. Observation of Apparent Dynamic Protonation and Deprotonization in CD4+T-Cell Model Systems
• Dynamic electrophoretic fingerprinting of the HIV-1 envelope glycoprotein
• Application note: Interactions of BSA with Alum